THE COLLOIDAL PROPERTIES OF SOIL 



TABLE XLII. NITROGEN IN BROADBALK WHEAT SOILS, 1893. 

 Per cent of dry soil. 



Lb. per acre. 



The Mechanism of Absorption. In a classical investigation 

 Way (298*2) argued that the absorption is purely chemical : the 

 ammonia and the calcium simply changed places as usual in 

 double decompositions or precipitations. He then proceeded 

 to discover the particular constituent of the soil with which the 

 reaction took place ; he found it was neither the calcium 

 carbonate, the sand, the undecomposed rock, however finely 

 ground, nor the organic matter. 1 The active constituent was 

 in the clay, but it formed only part of the clay, and, moreover, 

 it lost its power on ignition. No known simple silicates 

 showed these properties, but he prepared a number of " double 

 silicates " of lime and alumina, of soda and alumina, etc., that 

 did ; thus they reacted, like clay, with ammonium salts to 



1 It was subsequently shown by Konig (153) that soil organic matter has a 

 marked power of absorbing ammonia from ammonium sulphate. 



