Water-bearing formations, defined

The stiffness of a solvent is defined as UIV-P., where UA is the cohesive energy density and is the internal pressure (Section 3.3.1). Of the water-miscible solvents, only the two ethers, tetrahydrofuran and 1,4-dioxane, and the amide HMPT are non-stiff (entries in italics in the second column in Table 3.8). This property bears on the energetics of introducing a solute (an ion) into a cavity that has to be formed in the solvent to accommodate the solute—the larger the stif iess, the more energy has to be invested in the formation of the cavity. 

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