A new set of atomic and group refractions is proposed for fluoroperhalo compounds, based on refractivity data for 112 compounds carefully screened for evidence of purity. Molar refractions found for saturated perhaloalkanes are fitted to= tO. l%, and for terminally unsaturated perhalo olefins to &0. 27& The set employs single, invariant values for carbon and for fluorine, but multiple values, dependent on position, for the other halogens.
