“Great heavens! what a discovery! if he had really done what he says! But no; it is impossible. There is an abyss to cross, and chemistry is yet too young.” _Second letter, same date._ “M. Rassmann is mistaken.... He has never obtained racemic acid with pure tartaric acid. He does what M. Fikentscher and the Viennese manufacturers do, with slight differences, which confirm the general opinion I expressed in my letter to M. Dumas a few days ago.” That letter, and also another addressed to Biot, indicated that racemic acid was formed in varying quantities in the mother-liquor, which remained after the purification of crude tartars. “I can at last,” Pasteur wrote from Leipzig to his wife, “turn my steps again towards France. I want it; I am very weary.” In an account of this journey in a newspaper called _La Vérité_ there was this sentence, which amused everybody, Pasteur included: “Never was treasure sought, never adored beauty pursued over hill and vale with greater ardour.” But the hero of scientific adventures was not satisfied. He had foreseen by the examination of crystalline forms, the correlation between hemihedral dissymmetry and rotatory power; this was, to his mind, a happy foresight. He had afterwards succeeded in separating the racemic acid, inactive on polarized light, into two acids, left and right, endowed with equal but contrary rotatory powers; this was a discovery deservedly qualified as memorable by good judges in those matters. Now he had indicated the mother-liquor as a source of racemic acid, and this was a precious observation that Kestner, who was specially interested in the question, confirmed in a letter to the Académie des Sciences (December, 1852), sending at the same time three large phials of racemic acid, one of which, made of thin glass, broke in Biot’s hands. But a great advance, apparently unrealizable, remained yet to be accomplished. Could not racemic acid be produced by the aid of tartaric acid?