1916] Sharp : Soluble Salts and Soil Colloids 325 



lined above and on passing through the Pasteur filter yielded a 

 clarified solution which had not lost its power to deflocculate the 

 Davis soil. The writer is fully aware that conditions might arise 

 wherein such treatments would considerably modify the defloc- 

 culating power of the solute — for example, in case of very dilute 

 solutions where absorption by the soil and filter would be rela- 

 tively large and possibly of sufficient magnitude to markedly 

 diminish the quantity of deflocculant in the filtrate, which would 

 result undoubtedly in a decrease in the deflocculating power of 

 the solution. A similar reduction in deflocculating power of a 

 solution would also be likely to appear if a solution were sub- 

 jected to repetitions of the procedure described above. 



Despite the evidence above some doubt may still be enter- 

 tained as to the absence of significant quantities of OH-ions in 

 the films of water on the immediate surfaces of the colloidal 

 particles, especially in view of the probability that the colloidal 

 matter in the diffused soils consists largely of compounds of the 

 chemical nature of sodium silicate, which hydrolizes to some 

 extent in water and eventually gives rise to OH-ions, thereby 

 lowering the surface tension as described by Tolman'^ and like- 

 wise producing the conditions obtaining in the "natant" col- 

 loids of Hall and Morison.^'* Moreover, the results secured by 

 Briggs^^ on the absorption of alkali hydrates by silica tends to 

 confirm the proposed conception of "natant" colloids. If this 

 be the case, the rate of diffusion of these ions from the films into 

 the more dilute medium would be the factor determining whether 

 it would be possible to transfer a sufficient quantity of these 

 ions, by means of the solution, to be effective on the physical 

 condition of a second, otherwise untreated, soil. Under the condi- 

 tions of the experiment just cited, a contact period of two days 

 was allowed for such diffusion, which would appear to allow 

 ample time therefor. 



Furthermore, as observed by Whitney and Straw^** and others, 

 the fact that NaOH in certain concentrations tends to stabilize 



33 Loc. cit. 



34 Loc. cit. 



35 Journ. Phys. Chem., vol. 9, p. 617, 1905. 



36 Loc. cit. 



