1916] Sharp: Soluble Salts and Soil Colloids 317 



amount of material finally found in suspension. All of the 

 salt-and-water treatments yielded suspensions containing more 

 than ten times the suspended matter found in the water-washed 

 soil. From the evidence reported in the above table it seems 

 proper to infer that neither the nature of the added sodium salt, 

 nor the loss of calcium and magnesium from the soil, have much 

 part in the production of the defiocculated condition noted in the 

 salt-treated, water-washed soils. The data of Table VII are also 

 discussed later in their relation to the possible effects of NaOH 

 and the OH-ion on the physical condition of soils. 



The interchange of ions between the soil silicates and neutral 

 salt solutions like NaCl or NaoSO^, which seems to result in the 

 formation of new colloidal substances, also necessitates the simul- 

 taneous presence of free acid or of new salts of the free acid as 

 the calcium or magnesium salts, in the solution bathing the soil 

 particles. As previously discussed, both of these conditions have 

 been encountered in the supernatant liquid of a neutral salt 

 solution in contact with soil and also in the first portion of the 

 percolate coming through a soil to which a neutral salt has been 

 added. The constant presence of the free acid and its soluble 

 salts, together with more or less of the salt originally added, oc- 

 casions the maintenance of a flocculated condition of the soil 

 colloids, so that any additional colloidal matter which may have 

 been produced is not sufficiently effective on the physical char- 

 acter of the soil to be easily recognized. 



If it be assumed that new and additional colloidal material 

 is formed in the soil by virtue of the salt-and-water treatments, 

 then it is most likely in existence prior to the washing process, but 

 its effects on the physical condition of the soil are not manifested 

 until the surrounding medium has become sufficiently dilute, with 

 respect to salts, to allow of a more or less complete diffusion of the 

 soil colloids. The addition of the neutral salts either produces 

 new colloidal matter simultaneously with the chemical inter- 

 change of bases, which occurs independently of the washing with 

 water, or in some manner disintegrates the existing colloidal 

 aggregates. The former seems the more plausible, especially in 

 view of certain phases of the work herein presented. In addition 

 we also have evidence that the washing with water alone does not 



