PRINCIPLES AND DEFINITIONS 11 



From what has been said, it follows that dissymmetry, 

 or noii-siiperposability of mirror image on the original 

 object, can exist without any asymmetry, as in racemic 

 mixtures. Dissymmetric molecules have the possibility 

 of forming symmetric or asymmetric aggregates ; asym- 

 metry is the realization of one of these two potentialities. 

 It is, therefore, obvious that dissymmetry represents a 

 necessary pre-requisite condition for any asymmetric state. 



2. Optical and Geometrical Asymmetry. Asymmetry as 

 defined here should be distinguished from geometrical 

 asymmetry. A geometrically asymmetric figure is one 

 which possesses no element of symmetry, that is, no center, 

 no axis and no plane of symmetry, while dissymmetric 

 figures (in the sense of Pasteur) might possess a complex 

 system of axes of symmetry, although they cannot possess 



(Pasteur, 1884). According to our views, one half of a racemic aggregate 

 consists of the right and the other of the left form of molecules, before, as 

 well as after, crystallization. 



That Pasteur was mistaken in this particular point is evidenced by the fol- 

 lowing investigations. Ostwald (1889) has shown by electric conductivity 

 methods that, in dilute water solutions, racemic tartaric acid does not exist 

 as such but is entirely dissociated into its dextrorotatory and laevorotatory 

 components. Eaoult reached the same conclusion by cryoscopic methods. 

 Wyrouboff (1884), Jungfleisch (1884), and Errera (1898) pointed out that 

 the separate crystallization of antipodes from racemic tartrate depends on the 

 relative solubilities of the individual components and of the mixture. These 

 solubilities, in their turn, are controlled by the temperature. Thus, at ordi- 

 nary room temperature the antipodes are less soluble than the racemic mix- 

 ture, and they crystallize separately, while, at temperatures above 26° C, the 

 order of solubility is reversed, and the racemate crystallizes. 



4 Emil Fischer (1894) introduced the concept of asymmetric synthesis, that 

 is, of the production of molecules which exhibit a rotation of a given sign 

 with full or partial exclusion of the antipode. But the term asymmetry for 

 expressing the properties of aggregates of molecules was employed^ — for the 

 first time, it seems — by Japp (1898) in his well known address, "Stereo- 

 chemistry and Vitalism," which was followed by an interesting discussion in 

 ' ' Nature. ' ' Japp wrote that the simultaneous production of two opposite 

 asymmetric halves is equivalent to the production of a symmetric whole, 

 whether the two asymmetric halves be actually united in the same molecule, 

 as in the case of meso-tartaric acid, or whether they exist as separate mole- 

 cules in the loft and right constituents of racemic acid. This statement shows 

 quite clearly that the author conceived asymmetry as the property of the 

 aggregate of molecules and not as the configurational character of the indi- 

 vidual molecules (the term enantiomorph was used in this latter sense). 



