Racemic acid is an old name for an optically inactive or racemic form of tartaric acid. It is an equal mixture of two mirror-image isomers (enantiomers), optically active in opposing directions.

Its sodium-ammonium salt is unusual among racemic mixtures in that during crystallization it can separate out into two kinds of crystals, each composed of one isomer, and whose macroscopic shapes are mirror images of each other. Louis Pasteur was thus able to separate the two enantiomers by picking apart the crystals.

In a modern-time re-enactment of the Pasteur experiment it was established that the preparation of crystals was not very reproducible, the crystals deformed but that the crystals were large enough to inspect with the naked eye (microscope not required).

See also

• Tartaric acid

References

1. The reexamination of Pasteur’s experiment in Japan Yoshito Tobe Mendeleev Communications Electronic Version, Issue 3, 2003 DOI article Free access version with experimental details

References

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• Photochemical Decoration of Dislocations inside Crystals of Photochemical Decoration of Dislocations inside Crystals of Acenaphthylene. M. D. COHEN, I. RON, G. M. J. SCHMIDT & J. M. THOMAS*
• Physics Department Colloquium Matthew P. A. Fisher, Kavli Institute for Theoretical Physics, UC Santa Barbara Title: Quantum Choreography: Exotica inside Crystals Abstract can be found
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• Inside-Out Dolomite — Jones 77 (7): 539 — Journal of Sedimentary Inside-out dolomite crystals are unusual because their cores are younger Later, calcite or dolomite cement was precipitated inside the hollow crystals.