356 ANNUAL RECORD OF SCIENCE AND INDUSTRY. 



As to the question in how far the elements that have been 

 absorbed by the soil may be redissolved and carried away 

 again, Ileiden states 



(1) As to bases. The bases do not become entirely in- 

 soluble by absorption, but the amount of water required to 

 rcdissolve them is far greater than that in which they were 

 originally dissolved. The force with which the soil holds 

 the absorbed base is far greater than that which the water 

 can exert to remove it. 



(2) As to acids. Phosphoric and silicic acids are, like the 

 bases, redissolved to slight extent, but require for this pur- 

 pose very large quantities of water. Sulphuric acid is ab- 

 sorbed but little; nitric acid and chlorine scarcely at all; 

 and all three, but especially the two latter, are very easily 

 removed from soils by water. 



The Causes of Soil -Absorption 



Have been much discussed and experimented upon. The 

 main questions in dispute are as to how far they are physi- 

 cal, dependent upon surface attraction ; how far they are 

 chemical, due to chemical combination ; and what ingredi- 

 ents of the soil and what special circumstances decide the 

 absorption. The absorption of phosphoric acid seems to be 

 a chemical process dependent upon its combination with 

 lime and magnesia, and more especially with iron and alu- 

 mina. The absorption of silica seems likewise to be due to 

 chemical combination, particularly with lime and alumina, 

 to be decreased by humus, and hence greatest in soils con- 

 taining little organic matter. 



The Absorption of Bases by the Soil 



Has been lately studied by H. P. Armsby, with a view to 

 gain light upon the question as to how far this is due to 

 chemical and how far to physical causes. The view that 

 the prime cause of the absorption is a physical one surface 

 attraction has been held by several experimenters, as Lie- 

 big, Henneberg and Stohmann, Peters, and Brustlein ; while 

 the investigations of Way, Eichhorn, Rautenberg, Heiden. 

 Knop, Warrington, and Pilitz show clearly that chemical 

 changes are involved. The prevailing opinion has been that 

 these chemical changes consist mainly in the exchange of 



