326 University of California Publications in Agricultural Sciences [Vol. 1 



colloidal matter of a comparatively inert chemical nature forms 

 the basis of an argument which opposes the conceptions herein 

 presented, and which favors the view that the OH-ion may, after 

 all, play an important role in the diffusion of colloids. Thus, 

 systems composed of colloidal silver, lampblack, or relatively 

 pure organic substances in contact with NaOH probably do not 

 offer opportunity for the direct addition of the sodium or the 

 exchange of ions whereby sodium is taken up. a factor which 

 forms an essential link in the scheme proposed by the writer to 

 explain the effects of the alkali salts on soils. Also the experi- 

 ments of Bliss, cited by Whitney and Straw,"' give an indica- 

 tion that NaOH may be an effective agent, through the medium 

 of the OH-ion. No attempt is made, however, to deny the com- 

 plete ineffectiveness of the OH-ion, for it undoubtedly has an 

 important influence on the physical condition of colloids, as is 

 the case with many ions. But with regard to the physical condi- 

 tion of the salt-treated Davis soil, it is very evident that the 

 OH-ion is a factor of much less significance than the other ions 

 associated with it. 



The Precipitating Effect of Various Acids and Salts 



ON THE Soil Colloids 



There seemed some possibility that the presence of some ion 

 or ions, other than the OH-ion, in the soil solution might be held 

 accountable for the extreme diffusion of the NaCl + H^O soil 

 and soils similarly affected by other salt treatments. Conse- 

 quently an extensive series of test-tube experiments dealing with 

 the effects of various acids and salts on the soil suspension were 

 undertaken. The results of these tests are briefly referred to at 

 this time in their relation to the condition existing in the salt- 

 treated, water-washed soils. 



It was found that N/2000 ITCl and H,SO, perceptibly floccu- 

 lated the soil colloids, as compared with distilled water sus- 

 pensions of the same soil. To attribute this action wholly to the 

 H-ion of the acid would, in the writer's opinion, be erroneous, 

 for no doubt salts are immediately formed when the acid comes 



3' Loc. cit. 



