Compressibility equations for liquids: a comparative study

Various empirical equations used for expressing the compressive properties of liquids have been studied. Despite its popularity, the well-known equation attributed to Tait has several undesirable features; moreover, it is in fact not Tait's original equation, but is the result of an accidental misquotation by a later writer. Tait's original equation, when rearranged, leads to an equation of the form V0P/V0 - V = K0 + mP where K0 is the bulk modulus at zero pressure and m the slope of the bulk-modulus-pressure curve. The equations of Tumlirz and of Tammann are merely rearrangements of the above equation. The spurious version of the Tait equation, Hudleston's equation, MacDonald's equation and the Van der Waal equation of state are all asymptotic to it at zero pressure, and are practically equivalent to it over the normal range of application. The above equation is both the most accurate and the most convenient two-constant compressibility equation available. By the addition of a term in P2 the equation can be adapted to fit data for water up to 12 kb; a further term in P3 is needed to accommodate a wide range of organic liquids up to 12 kb.