1916] Sharp: Soluble Salts and Soil Colloids 303 



TABLE II 



Suspended Matter in Soils Which Have Received Various Treatments 



Per cent of 



Weight of Suspended 



Previous Suspending Suspended Matter 



No. Davis Soil Soil Treatment Medium Matter-grs. in soil 



1 40 grs. Washed with dis- 



tilled water HjO .3100 .77 



2 40 grs. Boiled in HoO HjO 2.5075 6.27 



3 40 grs. .290 grs. of NaCl 



washed out H,0 2.9555 7.39 



4 40 grs N/SONa.CO,, .2665 .66 



5 40 grs N/50NaOH 2.7975 6.99 



NaCl -)- HoO soil yielded 2.9555 grams, or nearly ten times the 

 amount of suspended matter found in the untreated soil. It is 

 an interesting coincidence that the rate of percolation previously 

 shown for the untreated soil is almost ten times that for soil 

 to which NaCl has been added and subsequently leached out. It 

 may be properly inferred from this that percolation varies in- 

 versely as the degree of diffusion, though our present knowledge 

 does not indicate a relation capable of expression in simple 

 mathematical terms. Furthermore, the inadequacies of the 

 method employed to secure the data in Table II make it impos- 

 sible to express a positive view with reference to the quantity of 

 colloids in the soils tested, but it is evident that the colloidal 

 matter present is in a much higher state of diffusion in certain 

 of the soils than in the control HoO soil. The three treatments, 

 boiling the soil in water, suspending it in NaOH of certain con- 

 centrations, and leaching added NaCl from it, produce approxi- 

 mately the same degree of diffusion in the soil colloids, as indi- 

 cated by the similarity in the results of the quantitative esti- 

 mations of the suspended matter derived from soils so treated. 

 This agreement in the behavior of the soils receiving the different 

 treatments suggests a similarity or possible relationship between 

 the processes by which these treatments affect the soil or soil 

 colloids. Boiling the soil in water has been assumed by soil 

 physicists to disintegrate the colloidal aggregates. If this be the 

 case and no new colloidal substances are formed by this pro- 

 cedure, then the similarity in colloidal content of the boiled soil 

 and the salt-treated, water-washed soil militates against the sup- 



