The determination of light refractive index is an important step in the characterization of liquid mixtures with different industrial applications. Through it, the purity of their substances can be assessed and, together with density and viscosity, it has a significant role in characterizing and understanding the thermodynamic properties of the liquids. Theaim of the present studywas to evaluate the accuracyofsomeofthe common mixingrules asappliedto the followingbinarymixtures: Benzene – Toluene, n-Heptane–n-Hexane, Chloroform – Benzene and Chloroform – Tolueneatdifferentconcentrationsandtemperatures.Themixtures were chosen becausedozens of millions of tonsof them areusedworldwide andthus they haveagreattechnologicalsignificanceandareessentialinalmostallaspectsofthe chemicalsynthesis.Inaddition, on the basisoftheresultsobtained,amodifiedequationbasedontheArago-Biotmixingrule was developed.The equationismoreaccurateandeasiertousethanmostexistingexpressionsinthe literature.