in carbon dioxide water. Almost all the phosphoric acid was re- 

 tained by the soil, while the greater part of the calcium went into 

 solution. The same results were obtained when hydroxides of 

 iron and aluminum were used instead of soil. 



Beyer and Biedermann 1 worked on the absorption of phos- 

 phoric acid by soils. Using a solution of sodium phosphate they 

 found no definite relation between the amount absorbed and the 

 quantities of iron, aluminum, and calcium contained in the soil, 

 though there was increased absorption with increased quantities 

 of these constituents. They determined the solvent action of 

 solutions of calcium sulphate, sodium chloride, sodium nitrate, 

 potassium chloride, and ammonium sulphate on the compound 

 formed by absorption. No appreciable effect was observed. 



Trochot 2 in his observations on volcanic soils noticed that 

 fair amounts of lime and phosphoric acid were present, and that 

 the fertility of these soils was very high in spite of their shallow- 

 ness. The conclusion was drawn that the lime rendered the 

 insoluble phosphates available. 



The fact that the phosphoric acid of superphosphate grad- 

 ually becomes insoluble in ammonium citrate solution was 

 observed by Millott 3 , and Joulie 4 . Millot found the change 

 to be due to the presence of large quantities of iron and alumium 

 oxides, while the results of Joulie seem to show that when an 

 insufficient quantity of sulphuric acid to completely decompose 

 the phosphate rock is used, (a condition which obtains in actual 

 practice) the change is due to the formation of tri-calcium phos- 

 phate. 



These experiments were extended somewhat by Albert and 

 Vollbrecht . They applied superphosphate to some soils con- 

 taining large amounts of lime, and to others containing small 

 amounts. With soils containing small quantities of lime, 6.5 

 per cent of the phosphoric acid of the superphosphate had become 

 insoluble in ammonium citrate after eight days, while with those 

 rich in lime, 15.4 per cent of the phosphoric acid had become 



i Chetn. Centr., 1869, 945. 

 2 Compt. rend., 81, 1027. 



3 Bied. Centr., 1875, 891879, 408. 



4 Ann. Chim. Phys., Series 5, 1879, 2 44- 



5 Bied. Centr., 1880, 84. 



