Racemic drugs: racemic mixture, racemic compound, or pseudoracemate?

Stereochemistry can be said to have begun in 1848 when Pasteur observed that crystals of sodium ammonium tartrate obtained by slow recrystallisation at room temperature were of two mirror image crystallographic forms. He was able to pick out these two forms by hand and show that solutions of equal concentration caused an equal and opposite rotation of plane polarised light. The rotation disappeared when the two crystal modifications were mixed in equal amounts before making a solution. This experiment provided the basis for the IUPAC rules for the nomenclature of organic stereoisomers, but also sowed the seeds for some of the current confusion regarding the correct description of racemic drugs in the solid state.