treated the mixture with different solvents. From his results lie 

 concluded that phosphoric acid in soils is almost entirely com- 

 bined with iron and aluminum, and that from a solution of cal- 

 -cium phosphate in carbon dioxide water, phosphoric acid is re- 

 moved by soils only when then the latter contain hydroxides of 

 iron and aluminum. Soils deprived of these compounds by treat- 

 ment with acids are apparently indifferent to the phosphate 

 solution. 



In studying the fixing power of soils for phosphoric acid 

 Voelcker 1 placed weighed quanties of six different kinds of loams 

 in bottles, and added known quantities of superphosphate solu- 

 tion. He noted from time to time the amount of phosphoric acid 

 still remaining in solution. The hydroxides present in the soils 

 varied from zero to 17.38 per cent, and the carbonate of calcium 

 from 0.15 per cent to 67.5 per cent. The phosphoric acid was 

 fixed with especial ease by those soils which contained a good 

 store of calcareous matter. The power of the clay soils to render 

 the soluble phosphoric acid insoluble was far less than that of 

 chalky soils. 



Warrington 2 determined the effect of several substances on 

 the solubility of freshly precipitated tri-calcium phosphate. He 

 found that one per cent solutions of ammonium chloride increased 

 the solubility in pure water, but that its addition to water sat- 

 urated with carbon dioxide produced practically no effect. He 

 observed also that when an excess of calcium carbonate was pres- 

 ent, the amount of tri-calcium phosphate dissolved by carbon 

 dioxide water was excessively small. The water became satu- 

 rated with calcium carbonate, while only trace of the phosphate 

 entered into solution. Kven a very small amount of calcium 

 carbonate was capable of producing this effect. 



Two years later 3 the same investigator carried out an elab- 

 orate experiment to show that the absorptive action of soil towards 

 phosphoric acid is due to the formation of insoluble phosphates, 

 by combination with hydroxides of iron and aluminum. Soils 

 freed from lime were treated with solutions of calcium phosphate 



1 Jour. Roy. Agr. Soc., 1863, 24, 46. 



2 Jour. Chem. Soc., 1866, 19, 296. 



3 Ibid., 1868, 21, i. 



