126 Phenomenon of Absorption in its Relation to Soils 



between solvent and absorbent presents in general the same character- 

 istics with soil as with other absorbents. 



The difference between the absorption of a base from a neutral salt 

 solution and of a dyestuff is that in the first case an equivalent of 

 other bases is always found in the solution after equilibrium is estab- 

 lished. This at first sight points to a chemical reaction in which two 

 insoluble bodies are concerned. 



As early as 1859 C. Boedeker^ setting out from Henneberg and 

 Stohmann's results formulated a mathematical expression for the 

 relationship between the ammonia absorbed by a soil and the calcium 

 turned out, which is substantially that obtained nearly 50 years after- 

 wards by A. D. Hall and C. T. Gimingham^. If we call the calcium 

 complex in soil Ca {X)^,, then on treating with ammonium chloride the 

 following reaction takes place: 



2NH4CI + CaZa z^ 2 (NH4) X + CaCU, 

 ah c d 



where a, b, c, d are the respective concentrations of the reacting sub- 



a^ 

 stances, then -,- = K, the active masses of the insoluble substances 



(L 



being constant. 



Hall and Gimingham found this law to hold with fair accuracy for 

 the reaction of china clay with ammonium chloride and they concluded 

 that a simple chemical reaction was a sufficient explanation of the 

 results obtained. 



Adolf Mayer^ had pointed out that Boedeker's equation does not 

 apply to the potassium results of Peters. Moreover the active mass 

 of the calcium represents also the amount of ammonia absorbed by the 



clay, and the equation -r "^ K therefore becomes a special case of the 



usual adsorption isotherm where P = 2. 



Attempts to explain the equilibrium results on physical lines have 

 been made by Patten, Cameron and Parker in the United States and 

 by Wiegner in Germany. Patten and Cameron in the paper quoted 

 above worked out Peters' potassium results and found them to be of an 

 adsorption type. E. G. Parker* working with potassium chloride and 

 J. H. Aberson^ working with ammonium chloride and soils obtained 

 similar results. 



1 Journ. f. Landw. 1859, 48. * Trans. Chem. Soc. 1907, 91, 677. 



3 Lehrbmh der Agriculturchonie, 1886. * J. Agric. Research, 1913, 1, 179. 



4 Kolloid Zeits. 1912, 10, 13. 



