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



three lines of argument, as outlined, may be closely allied or even 

 parallel, yet in view of our work they seem sufficiently well de- 

 fined to warrant a separate discussion of each. 



At the outset it may be said that it has been extremely diffi- 

 cult to find appropriate and reliable methods of attacking this 

 problem. Certainly opportunity is not lacking for future in- 

 vestigations to perfect accurate methods for definitely measuring 

 certain soil properties or soil constants, which are discussed 

 below. The Davis clay-loam soil was used throughout the fol- 

 lowing experiments, except as otherwise noted. The designation 

 NaCl -|- HoO used before the word soil signifies that the soil 

 was treated with from 0.2 to 0.5 per cent of NaCl, most or all 

 of which, together with the soluble salts formed, has been subse- 

 quently leached from the soil witli water. It must be added that 

 a quantity of Davis clay-loam soil was given the same amount 

 of washing with water to serve as a control soil, and hereafter 

 will be referred to as H^O soil. A comparison of the HoO soil 

 with unwashed Davis soil disclosed no important differences. 



Some Phtsico-Chemical Observations on the Salt-Treated, 

 Water-Washed Soil 



It seemed reasonable to expect that a stvidy of the NaCl + H._,0 

 soil itself would reflect, in some degree, the causes contributing 

 to the pronounced imperviousne.ss of such soils. Therefore, as 

 an introduction to this subject, determinations were made of the 

 suspended matter derived from soils which have been subjected 

 to various treatments, and they appear in Table II. The soils 

 and suspending media were placed together in tall hydrometer 

 jars, and were thoroughly shaken for 45 minutes. After standing 

 undisturbed for eighteen hours, aliquot portions of the sus- 

 pensions were removed by means of a pipette, evaporated to 

 dryness in platinum dishes, dried at 110° C, and weighed. 



The data reported in Table II confirm by an entirely different 

 procedure the original belief with respect to the intensity of the 

 diffusion of the colloids of the salt-treated, water-washed soils. 

 Under the conditions of the experiment 40 grams of normal soil 

 yielded 0.310 grams of suspended matter, while 40 grams of 



