Des cristaux d’Auguste Laurent et des techniques d’analyse optique de Jean-Baptiste Biot furent directement à l’origine de la découverte de la chiralité par Louis Pasteur / The crystals of Auguste Laurent and the optical analysis techniques of Jean-Baptis

The history of Louis Pasteur's separation of two kinds of tartaric acids is complicated, because (1) the names of the compounds discussed changed over time, (2) the notions of molecule and atom in the 19th century were not those we have today, (3) the historical texts are numerous and sometimes contradictory, as will be seen here by selected examples, and (4) many of the commentaries on Pasteur's work have been hagiographic or nationalistic, as early as Pasteur's lifetime. In particular, this article establishes that, contrary to popular belief, the separation of the two types of tartrate crystals present in the racemic mixture did not require particularly remarkable skill or vision, as has been stated; instead, Pasteur must have learned the techniques of crystallization, in order to form the crystals (which were several centimeters long) he was exploring by then- modern optical analysis techniques. Pasteur must above all be credited with persistence in his studies of this question, and his work is part of the long history of tartaric acid and tartrates during which Jean-Baptiste Biot and Auguste Laurent, in particular, played a primordial role, often underestimated. Finally, the recognition of the various tartaric acids and tartrates is neither the beginning nor the end of the history of chirality.