CHAPTER VIII. 



PASTEUR'S LAW. 



Pasteur's Discovery of the Fission of Racemic Acid. Mole- 

 cular Dissymetry and Optical Activity. - Fission-Methods. - 

 Spontaneous Crystallisation; Problems and Investigations. - 

 Transition-temperature. - - Partial Racemism. -- Physiological 

 action of Optical Antipodes. - - Enzyme- Action. - - Pseudo- 

 Racemism. Racemisation, its Mechanism and Equilibrium. - 

 Pasteur's General Conclusions. The Theory of the Asymmetric 

 Atom. - - Pasteur's Law and Van 't Hoff-Le Bel's Theory; 

 Problems and Investigations. - - The Symmetry of Chemical 

 Molecules. Crystallonomical Relations; Problems and Data. - 

 Chemical Composition and Optical Rotatory Power. -- Asym- 

 metric Metal-atoms. Enantiomorphism of Cyclic Compounds. 

 Enantiomorphous Configuration and Hemihedrism. Final 



Remarks. 



.... "Our knowledge of that aristocracy of chemical 

 compounds "which possess, in addition to all the 

 commonplace and -vulgar physical attributes, the dis- 

 tinctive seal of nobleness: optical activity." 



Percy Frankland. 1891. 



1. It was in 1848 that Pasteur, at the very beginning of his 

 scientific career, made his famous discovery that when the sodium- 

 ammonium-salt of racemic acid: C^0 6 H 6 , was recrystallised from an 

 aqueous solution at lower temperatures, it deposited two kinds of 

 crystals which were non-superposable mirror- images of each other. The 

 organic acids set free from both kinds of crystals after careful selec- 

 tion, appeared to have the same composition as the racemic acid itself. 

 But the one, if dissolved in water, made the plane of a linear polarised 

 beam of light passing through its solution deviate through a certain 



