Which Royal Society medal did Pasteur receive in 1856?

The Royal Society medal Pasteur received in 1856 was the Rumford Medal. London’s Royal Society awarded it for his work on the nature of racemic acid and its relationship to polarized light, a subject rooted in his early crystallographic research.

Pasteur’s key insight came from examining crystals of tartrate salts. He noticed that some crystals existed in mirror-image forms and painstakingly separated them by hand. Their solutions rotated polarized light in opposite directions. This provided important evidence that molecular arrangement could produce optical activity and helped establish the foundations of stereochemistry.

The award is sometimes confused with Pasteur’s later Royal Society honours. He received the Copley Medal in 1874 for his work on fermentation, while the Rumford Medal belongs specifically to his 1856 research on polarized light and racemic acid. His scientific interests later broadened from molecular asymmetry to fermentation, germ theory, pasteurization, and vaccines.