Foundations of Pasteur’s discovery of molecular chirality

In 1848, Louis Pasteur announced his discovery of a relationship between crystal form and optical activity in tartrate salts, which led to our modern concept of stereochemistry. This talk will cover three aspects of what was known in 1848 that served as the foundations of his discovery. These aspects are: (1) What was known about the relationship between shape, optical activity, and the chemical formula of crystals? (2) What was known about tartrate and paratartrate salts? (3) Who influenced Pasteur and led him to this research topic? Much of this talk will be based on scholarship conducted in the past by J. D. Bernal, Sy Mauskopf, and others, but in the course of putting this talk together I have made an interesting discovery. The first published observation of hemihedry in tartrate crystals was not made by Wilhelm Gottlieb Hankel in 1841, as has been thought until now, but rather by a British businessman and amateur crystallographer seventeen years earlier in 1824. This clear description of hemihedral tartrate crystals went unnoticed at the time and seems to have escaped the attention of historians ever since.