1916] Sharp : Soluile Salts and Soil Colloids 337 



debate. Hilgard" has consistently maintained that the power 

 of such colloids to remain in a stabilized condition is not to be 

 attributed solely to the fineness of division of such particles, but 

 that other factors may be responsible for that condition. In 

 agreement therewith, our experience, which has been presented 

 in this communication, has led us to believe that the chemical 

 nature of the body itself and that of the medium, determine in a 

 large measure the condition in which the colloid may exist. 



The extent to which the factor considered in this paper may 

 be applicable to agricultural practice can be better surmised than 

 asserted at the present writing, but it seem.s highly possible that 

 the modifications of the phj^sical condition of the soil, due to 

 washing out the soluble salts, under circumstances involving 

 fertilizer applications or natural alkali soils, will be reflected in 

 the inferior tilling qualities of the soil, in the increased resistance 

 offered by such soils to root penetration, in the lack of air space 

 and air movements, in the defiocculated soil, and in the moisture 

 and temperature relations of such diffused soils. The movement 

 of moisture in soils by surface tension and osmotic pressure or 

 under gravitational attraction, appears to be particularly de- 

 pendent upon the degree of deflocculation of the soil colloids. 



Besides affecting the physical condition of the soil, the leach- 

 ing out of soluble neutral salts from soils is, as has been previously 

 shown, frequently accompanied by notable quantities of calcium 

 and magnesium in the percolate. Thereby the soil sustains a con- 

 siderable loss of calcium and magnesium, which may in the course 

 of time be of sufficient magnitude actually to deplete the available 

 supply of these plant-food elements in the soil. The bacterial 

 flora and bacterial activity of soils subjected to the treatments 

 outlined above are liable to be considerably modified and to all 

 appearances in a harmful direction. Thus all the factors of soil 

 fertility are likely to be measureably affected through the pro- 

 cess of washing salts from soils ; consequently the crop-producing 

 power of the salt-treated, water-washed soil is apt to be con- 

 siderablv modified. 



73 Soils, chap. VI. 



