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<br />t <br />; <br />r' <br />~ <br /> <br />approaching equilibrium). A l:9 sediment-water mixture was shaken until <br />the increase in EC was minimal, that is, equilibrium was reached. Water <br />was then added until a 1,99 sediment-water mixture was achieved, and <br />with each dilution additional dissolved solids were obtained from the <br />sample. <br />Laronne (1977) also performed an additional experiment to <br />demonstrate the presence of undissolved material, as sediment <br />concentrations increased in three solutions. Equilibrated mixtures of <br />each solution were rapidly heated to 75oC. A comparison of the heated <br />to the unheated solutions (Table 2-4) shows that, as sediment <br />concentrations increased, the percent of additional dissolved ion <br />species due to heating increased. A marked increase of speci fic-ion <br />concentrations and SC took place in both 1,99 and 1.9 solutions. The <br />increase due to heating was greatest for Ca2+ in the 1.9 solutions and <br />for HC031- in the l,99 solutions. Because no significant difference <br />exists between the specific ion concentrations and the SC increase was <br />small for the 1.999 solution, it is inferred that most of the soluble <br />minerals dissolved upon contact in this dilute solution while it was <br />heated. <br />These experiments show that both 1.9 and 1,99 mixtures were <br />partially equilibrated, but they contained undissolved minerals. <br />Laronne (1977) suggests that this could be a result of the coating of <br />particles with siliceous or ferric oxide during precipitation of <br />evaporites. During the continuous concentration of the soil solution <br />due to evaporation, the slightly soluble minerals are the first to <br />precipitate out of the solution. Therefore, a slightly soluble mineral <br />such as gypsum would be expected to be surrounded by a more complete and <br />thicker coating than that deposited on the more soluble minerals such as <br />sulfates of sodium and magnesium, which begin to precipitate later. <br />Upon contact wi th water the most soluble minerals, those least coated <br />with the slightly soluble ferric oxides, dissolve rapidly and more <br />completely than gypsum or calcite. Moreover, if the coating is thick <br />some of the particles of gypsum and calcite may not dissolve in the soil <br />solution, because the solution may be saturated with respect to a ferric <br />oxide, although it is undersaturated with respect to gypsum. <br /> <br />, <br />'I <br />'I <br />:1 <br /> <br />2$ <br />