ABSORPTIVK POWER OF TUE SOIL. 349 



ide of iron which llie soils yielded to hydrochloric acid. 

 Heiden traced a similar relation between the silica set free 

 by the action of acids on cluven soils and their absorptive 

 power. Rautenberg and Heiden further confinued what 

 Way and Peters Imd previously shown, viz., that treat- 

 ment of soil with acids diminished their absorbent power. 

 These facts admit of interpretation as follows : Since 

 neither silica, hydrated alumina, nor hydrated oxide of 

 iron, as such, have any absorptive or decomposing power 

 on suljihates, nitrates, etc., and since these bodies do not 

 ordinarily exist as sncli to much extent in soils, therefore 

 the connection found in twenty cases to subsist between 

 their amount (soluble in acids) in the soil, and the ab- 

 sorptive power of the latter points to a compound of 

 these (and other) substances (silicate of alumina, iron, 

 lime, etc.), as tlie absorptive agent. 



That the absorbing compound is not necessarily hydra- 

 ted, is indicated by the fact that calcination, wliich must 

 Temove water, though it diminishes, does not always alto- 

 gether destroy the absorptive quality of a soil. (See p. 

 343.) Eiciihorn, as already stated, found that the anhy- 

 drous silicates, chlorite and labradorite, Avere acted upon 

 by saline solutions, though but slowly. 



Do Zeolitic Silicates, hydrated or otherwise, exist 

 in the Soil? — When a soil which is free from carbonates 

 and salts readily soluble in water, is treated with 

 acetic, hydrochloric, or nitric acid, there is taken up a 

 quantit-y (several per cent.), of matter Avhich, while con- 

 taining all the elements of the soil, consists chiefly of 

 alumina and oxide of iron. Silica is not dissolved to much 

 extent in the acid, but the soil which before treatment 

 with acid contains but a minute amount of uncoinbined. 

 silica, afterwards yields to the ))roper solvent (hot solution 

 of carbonate of soda) a considerable quantity. This is our 

 best evidence of the presence in the soil of easily decora* 



