112 JOURNAL OF THE 



phosphate is applied to the field the original phosphoric acid 

 com pounds of the phosphate no longer remain unaltered, but 

 rapidly assume other forms and enter into new combinations. 

 Xor will any special discussion be entered upon as to the exact 

 chemical compounds which are formed by this change, beyond 

 those which may be classified under the general heads of soluble, 

 insoluble, and reverted phosphates. 



That superphosphates, after being applied to the soil, when 

 partly dissolved by rains are not leached from the soil, as is the 

 case with some soluble compounds, such as kainit or ammonia 

 salts, is well known. H. Von Liebig* has shown by analysis 

 of the soil and subsoil at Rothamsted of certain plots of land 

 which had received 350 pounds of superphosphate per acre 

 yearly for a period of 22 years that in the first nine inches of 

 the soil three-fourths of the total amount of the phosphoric 

 acid found were present; in the next nine inches the remainder 

 was found ; while below this no appreciable quantity was detected 

 over the natural contents of the soil. It is seen, therefore, that 

 out of a total amount of nearly 40 tons applied to the acre dur- 

 ing these years none of the soluble phosphoric acid of the super- 

 phosphate had been leached or diffused below a depth of eighteen 

 inches, and nearly all had remained less than a foot below the 

 surface. From the result of this examination it is readily seen 

 that the soil prevents excessive diffusion of the soluble phos- 

 phoric acid and precipitates it by the action of some of its com- 

 ponent parts, in forming less soluble compounds. The cause of 

 this precipitation is due to the presence of lime,f also to the 

 sesquioxides of iron and alumina, X and to some extent silica and 

 silicious matters. § 



The precipitation in the case of lime salts is undeniably fast; 

 so much so that Wagner^f thinks that is so great that no diffu- 

 sion of any kind can exist. While this may be true of soils 



*Journal Royal Agricultural Society, 17, 1881, 281. 

 fVoelcker, Journ. Roy. Ag. Soc, 16, 1, 153. 

 JMillot, Jour. d'Ag. Prat., '74, 1, 166. 

 gColson, Bull, de la Soc. Chem., '80, p. 153. 

 ^[Lehrbuch der Duiingerfabrikation, '87, 63. 



