228 SCIENCE PROGRESS 



Having thus established the truth of the idea that asymmetry 

 and enantiomorphism mark the property of optical activity, he 

 went a step further, and pointed out that the asymmetry was 

 due to the arrangement of molecules (or groups of molecules) in 

 the crystal in the case of quartz, sodium chlorate, etc., which 

 lost their activity with the crystalline structure, and to the 

 arrangement of atoms in the molecule, in the case of tartaric 

 acid, etc., which were active in the liquid or dissolved state. 



The asymmetry of the crystal could be easily understood as 

 a direct result of the presence of the facets, without any 

 hypothesis as to the particular arrangement of the molecules in 

 the crystal. But to explain molecular asymmetry some hypo- 

 thesis as regards the arrangement of atoms seemed to be 

 necessary. 



"Are the atoms of right-handed tartaric acid," asks Pasteur, 

 " arranged along the spiral of a right-handed screw, or are they 

 situated at the corners of an irregular tetrahedron, or have they 

 some other asymmetric grouping? " He is very diffident about 

 the true answer, and remarks, " We cannot answer these 

 questions. But of this there is no doubt, the atoms possess an 

 asymmetric arrangement, having a non-superposable image." 1 



The step, which Pasteur hesitated to take, Van't Hoflf took 

 soon after, and explained molecular asymmetry or enantiomor- 

 phism, and consequently also optical activity in the liquid or 

 dissolved state, by assuming the tetrahedral grouping, which is 

 almost universally accepted at the present time. 



Thus the idea, that enantiomorphism or asymmetry in a 

 molecule is necessarily present when a substance is active in 

 the dissolved condition, was thoroughly established, and has 

 been abundantly confirmed by later research. 



Chemists, however, have gone further. They have assumed 

 first that enantiomorphism is the cause of optical activity, and 

 secondly, as a corollary of this, that when a molecular con- 

 figuration is asymmetric and enantiomorphous, the substance 

 represented by that configuration must be necessarily optically 

 active (or capable of being resolved into optically active 

 isomers). 



These assumptions seem to the writer to be quite un- 

 justifiable. 



In the first place, the evidence of crystallography, from which 

 1 Alembic Club Reprints, No. 14. 



