Heated crystals jump to enantiomeric separation

Louis Pasteur’s 1848 experiment that established the hypothesis of molecular chirality is rightly regarded not just as a landmark in structural chemistry but as a paradigm of patience. To separate the two enantiomers of sodium ammonium tartrate, which spontaneously segregated during crystallisation to form mirror-image asymmetric crystals, Pasteur risked eye-strain as he apportioned the little chiral crystals into two piles using tweezers. (The word ‘chirality’, from the Greek for ‘hand’, came decades later, coined by Lord Kelvin in 1893.)