SCIENCE PROGRESS 

 <100H 



OH HO. 



H H 



doOH 



OH H 



An equimolecular mixture of (i) and (2) gives racemic acid. 



One point must be noticed. It might be supposed that if the 

 two tetrahedra in the tartaric acids were to revolve around their 

 common axis, the one isomer could be changed into the other, 

 but this is not the case. The configuration of each isomer 

 depends upon the order in which the groups are disposed 

 around the tetrahedron, and no revolution can alter this. It 

 is assumed that in these isomers the two tetrahedra can vibrate 

 quite freely ; but it is probable that, under any given conditions, 

 they will come into equilibrium in some fixed position. 



In order to make clear the difference in physical properties 

 which is produced by differences in the arrangements of atoms 

 in space, a table is given below which includes the chief proper- 

 ties of the dextro, laevo, meso, and racemic forms of tartaric acid : 



Melting-point 

 Affinity Constant 

 Specific Gravity 

 Solubility in 100 parts ( 

 of water at 15° i 



We must now consider what influence is exerted upon certain 

 reactions by these differences in the spacial arrangements of 

 atoms ; and, in the first instance, we may deal with the actions 

 of certain organisms upon racemic compounds. It has been 

 observed by many observers,^ of whom Pasteur was the pioneer, 



^ This is probably not the true value for K, as in dilute solutions the racemic 

 acid dissociates into the two antipodes. 



^ A complete set of references is to be found in Landolt's Optische Drehuttgs- 

 vermogen organischer Substa?izen, Brunswick ; or inWinther, Ber., 28, 3022 (1895). 



