Molecular Refraction Experiment and Calculation

The electronic polarization (P ) of a molecule is not only useful to calculate the atomic component of the molar polarization and the dipole moment, but is of independent interest for studying the bonding type and structure of a substance. Among chemists the Pe determined according to Eq. 11.14 is commonly known as the refraction , R, and is expressed in non-SI units, cm /mol, whereas physicists prefer to use polarizability a, expressed in A, so that formally a = 0.3964 R (a is also expressed in atomic units, 1 a. u. = 0.148185 A ). For uniformity, is measured with the 589 nmNa line (Ru) or is extrapolated to infinitely long waves (Poo), unless the entire dispersion spectrum of RI is determined. 

Besides Eq. 11.14, there are other formulae for refraction. Newton [95] introduced the concept of refraction into science at the beginning of eighteenth century and gave in his Optics the first formula expressing the refraction in terms of refractive index and density (volume). 

He subjected this formula to a great number of tests, some of which involved a thousand fold variation in density, and found the refraction remaining constant to within one order of magnitude, with a mean deviation of 33 %. In 1853, Beer [96] expressed the opinion that for gases the quantity 

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Having obtained the value of the refracdve index from the tables, and the density of the liquid at the temperature of the experiment having been determined (p. 43), the specific and molecular refractivities can be calculated by means of the formulte—... 

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