Racemic acid


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, optically active in opposing directions. The naturally occurring form of the acid is the right-handed.
Tartaric acid's 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. Thus, Louis Pasteur was able before 1850 to separate the two enantiomers by picking apart the crystals. Pasteur announced his intention to resolve racemic acid in:
while he presented his resolution of racemic acid into separate optical isomers in:
In the latter paper, Pasteur sketches from natural concrete reality chiral polytopes quite possibly for the first time. The optical property of tartaric acid was first observed in 1832 by Jean Baptiste Biot, who observed its ability to rotate polarized light. It remains unknown whether Arthur Cayley or Ludwig Schläfli, or other contemporary mathematicians who studied polytopes, knew of the French work.
In two modern-day re-enactments performed in Japan of the Pasteur experiment, it was established that the preparation of crystals was not very reproducible. The crystals deformed, but they were large enough to inspect with the naked eye.