Molar refractivity

Molar refractivity, ${\displaystyle A}$, is a measure of the total polarizability of a mole of a substance and is dependent on the temperature, the index of refraction, and the pressure.

The molar refractivity is defined as

where ${\displaystyle N_{A}\approx 6.022\times 10^{23}}$ is the Avogadro constant and ${\displaystyle \alpha }$ is the mean polarizability of a molecule.

Substituting the molar refractivity into the Lorentz-Lorenz formula gives

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