The diastereomer formation interaction is used as the resolution of racemic modifications, i.e., the separation of racemic modifications into enantiomers. A racemic modification is a mixture of equal parts of enantiomers and is optically inactive. Enantiomers making up the racemic modification have identical physical properties (e.g., boiling points, relative densities, refractive indexes, etc.) and hence cannot be separated by usual methods of fractional distillation or fractional crystallization. Addition of an optically active base, L-base, to a racemic acid (mixture of D- and L-acid) will result in a mixture of two salts, diastereomer salt D-L and diastereomer salt L-L, which are diastereomer isomers of each other. They can be sepa- rated by usual resolution procedures, e.g., fractional crystallization and fractional distillation, since diastereomers have different physical properties