Refractive dispersion of organic compounds VII-The refractive indices of the hexane and the refractive of hydrogen and carbon. Significance of the dispersion constants

Abstract

The law of additivity as applied to molecular refractions is based on two empirical observations, both of which were first established quanti-tatively by Landolt,* namely, (i) the constancy of the increment of molecular refraction corresponding to each addition of CH 2 in a homologous series, and (ii) the identity of the molecular refractions of Homeric compounds. With the help of this law the refractivity of a molecule may be resolved into the sum of a series of atomic refractivities. Thus Eisenlohr in 1910 calculated the refractivities of carbon and hydrogen, for the D-line of sodium and for the three visible 1ines of hydrogen, from measurements of the refractive indices at these wave-1engths of 145 open-chain hydrocarbons, aldehydes, ketones, acids, alcohols, and esters, as foIlows: (i) The refractivity of the methylene radical R[CH 2 ] was deduced from the mean increment between consecutive members of various homologous series. (ii) The refractivity of was deduced by extrapolation from the refractivities of the series of paralffins by means of the relation R[H 2 ]=R[C n H 2 n +2 ]- n R[CH 2 ].