12 



accessible but abstracts give the following conclusions. ' 'Sand 

 offers no resistance to the extraction of the phosphoric of super- 

 phosphate by water. Addition of orthoclase produces no effect. 

 Calcium carbonate combines quickly with soluble phosphoric 

 acid. Iron and aluminum hydroxides are also active in retain- 

 ing phosphoric acid. The compounds formed with iron and 

 aluminum are more stable towards salt solutions than tri-calcium 

 phosphate. Sodium chloride solutions (i per cent and 2 per 

 cent) dissolve less phosphoric acid from superphosphate than 

 pure water. In the presence of calcium carbonate and hydroxi- 

 des of iron and alumium the salt solutions dissolve more than 

 pure water. ' ' 



The action of carbon dioxide on tri-calcium phosphate alone 

 and in the presence of ferric hydroxide was studied by Geogievice 1 . 

 Tri-calcium phosphate suspended in water was decomposed by 

 carbon dioxide, but the reaction was far from being complete. 

 When ferric hydroxide was also present decomposition took place, 

 but the phosphoric acid immediately combined with the iron. 

 Under some conditions the whole of the phosphoric acid was with- 

 drawn from the calcium salt. These results confirm the observa- 

 tions of many previous workers, namely, that all of the phosphoric 

 acid in calcium phosphate when applied to the soil finally becomes 

 converted to phosphate of iron. 



Some interesting facts regarding the assimilation of phos- 

 phoric acid by crops were obtained by Deherain 2 on the experi- 

 mental plots at Grignon. He noticed that the sum of the phos- 

 phoric acid in drainage and crops in ten years, was not equal 

 to the phosphoric acid not extracted by acetic acid. He con- 

 cluded that the calcium phosphate was changed to iron and 

 aluminum phosphates after a time. A soil was mixed with tri- 

 calcium phosphate and placed in a seltzogene. After a few days 

 no phosphoric acid was dissolved by water charged with carbon 

 dioxide, although tri-calcium phosphate is soluble in this mix- 

 ture. He does not state whether the soil contained lime. Ferric 

 and aluminum phosphates were assimilated by oats but not by 

 wheat. 



1 Monatsh., 1891, 12,566. 



2 Ann. Agron., 17, 445. 



