Chirality[edit]
This seems to be the case with Pasteur's discovery that chemically identical molecules can have chirality (the way a right handed baseball glove will not work with the left hand). Roberts writes "Pasteur was puzzled: the salts of tartaric acid and racemic acid were said to be identical in chemical composition and crystalline shape, but they had different effects on polarized light."[1] Pasteur later prepared a solution of only racemic acid and found that it itself contained salt crystals with chirality and which affected light differently. This was somewhat lucky because the type of salt crystals that Pasteur was studying (sodium ammonium salt of racemic acid) is one of few salts that would be visibly different in Pasteur's time. Moreover, the salts only differentiate if the solution reaches a temperature below 26 °C (79 °F); Pasteur did not know about this temperature requirement, but he did happen to store the solution on a window sill over night and the cold Paris air activated it.[1]