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Pasteur was fourth on the list of those admitted to the Ecole Normale, where he started work with enthusiasm. During his holiday breaks he arranged to give lessons on physical science at Barbet’s school. Louis had grown into a grave, quiet, rather shy young man, tall and thoughtful, but full of dash and fire under this reserved façade. He read widely and his letters to his family show that he was very happy at this time. Crystals and Light Rays Pasteur was in the habit of taking long walks in the Luxembourg Gardens with his companion, Chappuis. On these walks they discussed everything—philosophy, history, and science. One day Pasteur began to talk about tartaric acid , which had been discovered in 1770 by the Swedish chemist Carl Wilhelm Scheele. When polarized light is passed through solutions of tartaric acid, the solution can turn the plane of the light to the right. So can solutions of ordinary sugar and crystals of certain quartzes. Some other substances, such as turpentine or quinine, rotate polarized light to the left. A rather mysterious substance called “racemic acid” had been studied by Joseph Louis Gay-Lussac and Jacob Berzelius. Chemically it looked similar to tartaric acid, but it did not rotate

For a short explanation of the effect of polarized light on racemic mixtures, scan here:

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