1916] Sharp : Soluble Salts and Soil Colloids 305 



surface for the deposition of hygroscopic moisture and for dye 

 adsorption, and since these phenomena are presumably direct 

 functions of surface the soils under observation should therefore 

 register increased hygroscopicity and dye adsorption. The find- 

 ings to the contrary cast some doubt on the validity of these 

 measurements as a reflection of the quantity of colloidal matter 

 present or its degree of diffusion. A third method suggests 

 itself, that developed by Mitscherlich,'' to study the interior sur- 

 face through energy exchanges when the soil is moistened with 

 water, but this has not as yet been tried. 



The use of the centrifugal machine as employed by Briggs 

 and McLane' to ascertain the moisture equivalent of soils in the 

 study of the salt-treated, water-washed soils, has yielded some 

 highly satisfactory results which will be reported in a future 

 paper. The method proposed by Lynde and Dupre^ for esti- 

 mating the capillary powers of soils has not proven entirely 

 satisfactory in our hands, when employed for investigating the 

 properties of the salt-treated soils. 



It was further questioned whether the physical condition of 

 the soil had been permanently changed or whether the injured soil 

 would completely recover its original condition in response to a 

 second addition of NaCl. Such a supposition naturally implies 

 that some of the reactions involved in producing the increased 

 diffusion partake of the nature of reversible reactions. In order 

 to test this point from a chemical standpoint, it would be neces- 

 sary to treat the injured soil with its own percolate. Work of 

 this character is reported under the second series of experiments. 

 In this connection, however, the effects of the added salts were 

 considered chiefly in their physical aspects, and accordingly the 

 following experiment was performed : Three grams of NaCl + 

 HoO soil were suspended in 10 cc. of NaCl solutions of various 

 concentrations in test-tubes. The time required to clear the 

 supernatant liquid denoted the effect of the NaCl. A similar 

 comparative series with HoO soil was also prepared. The results 

 are given in Table III. 



•J Bodenkunde fiir Land- und Forstwirte, p. 51. 



7 U. S. Dept. Agr., Bur. of Soils, Bull. 45. 



8 Journ. Amer. See. Agron., vol. 5, no. 2, p. 107, 1913. 



