ABSORrXIVE POWER OF THE SOIL. 337 



Experiments to ascertain how much of a substance the soil Is able to 

 absorb are made by putting a known amount of tbc drij soil (e. g. 100 

 grms.) in a bottle with a given volume (e. g. 500 cubic cent.) of solution 

 whose content of substance has been accurately determined. The solu- 

 tions are most conveniently prepared so as to contain as many grms. of 

 the salt to the liter of water as corresponds to the atomic weight or 

 equivalent of the former, or one-half, one tenth, etc., of that amount. 

 The soil and solution are kept in contact with occasional agitation for 

 some hours or days, and then a measured portion of the liquid is 

 filtered off and subjected to chemical analysis. 



The absorptive power of tlio soil is exerted unequally 

 towards individual substances. Thus, in Peters' experi- 

 ments ( Vs. St., II., 140), the soil he operated with absorb- 

 ed the bases in quantities diminishing in the following 

 order : 



Potash, Ammonia, Soda, Magnesia, Lime. 

 Another soil, experimented upon by Ktillenberg 

 {Jahresbericht ilber Agricidtur. Chemie, 1865, p. 15), ab- 

 sorbed in a different order of quantity, as follows : 

 Ammonia, Potash, Magnesia, Lime, Soda. 



As might be expected, different soils evert ahsorptive 

 •power toioards the same substance to an u)iequal extent. 

 Kautenberg {Henneberg' s Jour, far Landicirthsrhaft, 

 18G2, p, 62), operated with nine soils, 10,000 parts of which, 

 under precisely similar circumstances, absorbed quantities 

 of ammonia ranging from 7 to 25 parts. 



The time required for absorjytion is usually short. 

 Way found that in most cases the absorption of ammonia 

 was complete in half an hour. Peters, however, observed 

 that 48 hours were requisite for the saturation of the soil 

 he employed with potash, and in the ex2:)eriinents of Hen- 

 neberg and Stohmann {Uenneberf s Jourmd.^ 1859, p. 35), 

 phosplioric acid continued to be fixed after the cxpiiation 

 of 24 hours. 



The strength of the solution influences the extent of 

 absorjition. The stronger the solution., the more subsia)tce 

 is taken up from it by the soil. Thus, in Peters' experi- 

 15 



