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. Thus, Louis Pasteur was 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 they were large enough to inspect with the naked eye (microscope not required).
- George B. Kauffman & Robin Myers (1998). "Pasteur's Resolution of Racemic Acid: A Sesquicentennial Retrospect and a New Translation" (PDF). The Chemical Educator 3. doi:10.1007/s00897980257a.
- Yoshito Tobe (2003). Free access version with experimental details "The reexamination of Pasteur's experiment in Japan" (PDF). Mendeleev Communications Electronic Version (3). doi:10.1070/MC2003v013n03ABEH001803.
- Masao Nakazaki (1979). "Morphology of sodium ammonium tartrate: Pasteur's spontaneous resolution and its reexamination". Kagaku no Ryoiki 33: 951–962.