236 PRINCIPLES OF AGRICULTURAL CHEMISTRY 



different soils. We give, in the following table, some results 

 secured with 100 grams soil in contact with 250 cc. solution con- 

 taining 0.07 gram calcium sulphate three days, and equivalent 

 quantities of the other salts: 



Percentage absorbed 1 



N H 3 from ammonium sulphate 60 



K. 2 O from potassium sulphate 55 



Na 2 O from sodium sulphate 19 



MgO from magnesium sulphate 46 



CaO from calcium sulphate 26 



P 2 O 5 from sodium phosphate 17 



SO 3 from sodium sulphate o 



Cl from sodium chloride o 



All soils appear to absorb phosphoric acid, potash, and am- 

 monia; but lime, magnesia, etc., are not always absorbed. For 

 instance, Biedermann 2 found that two out of nine soils absorbed 

 lime, six absorbed magnesia, one absorbed sulphuric acid, and all 

 absorbed phosphoric acid and potash. 



The form of combination has also some effect upon the amount 

 of absorption. For example, if we compare ^different salts of 

 potash, such as the chloride, nitrate, and sulphate, we find differ- 

 ent amounts of potash absorbed. 



Percentage 

 K 2 O absorbed 



Potassium phosphate 57 



Potassium carbonate 65 



Potassium chloride 57 



Potassium sulphate 55 



Potassium nitrate 51 



(2) The Nature of the Soil. Sands, as a rule, have low 

 absorptive powers; loams and clays, much higher. The absorp- 

 tive power of the same soil depends upon the substance used to 

 measure it. For example, it is different for potash and for phos- 

 phoric acid. 



In the following table, the absorptive power is measured by the 

 percentage of ammonia absorbed by 50 grams soil from a solu- 

 tion of one gram ammonium chloride in 208 cc. water. 



1 Bretschneider, Jahresber, f. Agr. Chem., 1868, p. 17. 



2 Jahresber, f. Agr. Chem., 1867, p. 77. 



