1916] Sharp: Soluble Salts and Soil Colloids 331 



a small quantity of salt remained in contact with the soil. These 

 observations lend further confirmation to the fact previously ob- 

 served, that a second addition of NaCl to a NaCl -f- HoO soil 

 does not cause the reversion of the soil to its original condition. 



General Discussion of the Effects Noted and Their 



Application to Soil Studies and the 



Management of Soils 



In the discussion on the possible relation of the calcium and 

 magnesium content of the percolate to the diffused conciition of 

 salt-treated, water-washed soils, attention has already been 

 called to the fact that the phenomena, first observed in case of 

 the cylinders containing Davis soil, also appeared in three other 

 soils of widely different types. Evidently the effects observed 

 when added salts are washed from soils by distilled water, are 

 not peculiar to any particular type of soil, but are more or less 

 general in their application. Some soils, as those which do not 

 offer replaceable calcium or magnesium to exchange for sodium 

 or other ions of salt solutions, would probably react to a much 

 less extent than those soils which do react with salt solutions. 

 The degree to which the soil is affected by the salt-and-water 

 treatments is apparently dependent upon the amount of exchange 

 of bases, or the direct addition of bases which occurs. This, of 

 course, varies markedly wnth different soil types and is probably 

 closely associated with complex silicates of which mention has 

 already been made. This conception conforms, in the main, with 

 the ideas brought out by Knop,"^* Van Bemmelen," and Waring- 

 ton,^*' with respect to the absorption of salts by soils. Moreover, 

 Kossovich" has noted that NaCl exercises a more pronounced 

 effect on capillary rise in clay soils than in sandy soils. 



There can be but little doubt that the effects of salts on the 

 physical and chemical properties of soils has a wide range of 

 application to alkali soils and their management. Moreover, the 



54 Cited from U. S. Dept. Agric, Bur. of Soils, Bull. 52, p. 19. 



55 Loc. cit. 



56 Loc. cit. 

 5" Loc. cit. 



