Thermoelectric differential vapor pressure lowering

Recall Eqs. 2-68 and 2-78). Direct measurement of A P is difficult because of the small magnitude of the effect. (At lOg/liter concentration in benzene, a polymer with M equal to 20,000 produces a vapor pressure lowering of about 2 x 10 mm Hg at room temperature. The limits of accuracy of pressure measurements are about half this value.) It is more accurate and convenient to convert this vapor pre.ssurc difference into a temperature difference. This is accomplished in the method called vapor phase osmometry. The procedure is also known as vapor pressure osmometry or more accurately as thermoelectric differential vapor pressure lowering. 

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