The energy of interaction between a hydrocarbon and a metal increases rapidly in the order copper, silver, lead, and iron (Fig. 8), and with the value ofP/P0. Tables Ia and Ib give the values of the energy atp/p0=1; i.e., at saturation of the vapor. The values of the work of adhesionWAat 25deg;C for the clean metals are copper 69, silver 77, lead 89, iron 93. For the oxide coated metals the values are only slightly higher (Table Ib). These increase with decrease of temperature. Fornhyphen;hexane they are essentially the same at 0deg;C as fornhyphen;heptane at 25deg;C. Isotherms fornhyphen;heptane are given for both 25deg;C and 15deg;C. Figure 7 illustrates a common phenomenon: a firsthyphen;order change at 0.02hyphen;mm Hg on clean silver.The method in general use for calculation of the work of adhesion from the adhesion tension is absurd, since for the usual case in which the liquid wets the solid the work of adhesion is given as twice the free surface energy of the liquid. Thus this states that the nature of the solid has nothing to do with the work of adhesion. Unfortunately, all of the books on surface chemistry give this entirely fallacious method of calculation. On this account it is recommended that the use of adhesion tension should be abandoned, since it is one of the most prolific sources of error in Surface Science.
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