1916] Sharp: Soluble Salts and Soil Colloids 323 



point must have been encountered at which the OH-ion concen- 

 tration of these two was the same or approximately so. Yet the 

 two salts exercised a different influence on the soil colloids at all 

 the concentrations used, with the exception of the highest and 

 lowest concentrations. This fact indicates that some other factor 

 than the OH-ion is effective in determining the degree of dis- 

 persion of the soil colloids. What application this may have to 

 black alkali lands is a question, for under natural conditions it is 

 most likely that all three compounds, NaOH, NallCO,, and 

 NaoCOg, and their respective ions occur. 



But the most striking feature of this phase of the problem 

 lies in the fact that the washing out of the soluble matter from 

 separate portions of the Davis soil receiving NaOH, NaoCOg, and 

 NaHCOo results in the same way. The soil becomes very im- 

 pervious and diffuses when shaken wuth distilled water. Thus 

 the cylinder soils receiving NaoCOg have been exposed to condi- 

 tions permitting the leaching out of the soluble salts, at least 

 from the surface soil, so that they now exhibit the same peeulari- 

 ties as the soils treated analogously in the laboratory. 



The systems so far considered have been largely made up of 

 soils to which various quantities of NaOH, NaaCOg or NaHCOg 

 have been added. To ascertain to what extent the facts so gained 

 are applicable to the conditions existing in the laboratory sam- 

 ples of NaCl -|- HgO soil or to those of the field cylinder soils 

 receiving NaCl and Na2S04, necessitates the measurement of the 

 all\:alinity obtaining in these soils. AVe have attempted to secure 

 some information with regard to the quantity of OH-ions or the 

 alkalinity in the solution containing a suspension of the 

 NaCl + H„0 soil, but the persistent color of this solution has 

 made it impracticable to employ it directly with the various indi- 

 cators. It would seem, however, from actual titrations made in 

 the usual manner using methyl orange as the indicator, that the 

 alkalinity of the soils in the cylinders receiving NaCl and Na2S04 

 had been somewhat increased over that of the control soils. But 

 solutions secured from soils treated in the laboratory in a manner 

 similar to the treatment of the field soils failed to verify con- 

 sistently the above observations. At the present time we are en- 

 gaged in a study of the reaction of the soil suspensions by the use 



