be obtained, which itself is also endowed with rotatory power. 

 Whether this will be greater or smaller than that of the original 

 substance, cannot be predicted, because general rules concerning 

 the influence of the chemical nature of substitutes on the size 

 of the specific or molecular rotation of the molecule in solution, 

 have up till now not been established with great success. l ) As 

 already mentioned, a number of experimental investigations of 

 this kind have been made by G u y e, W a 1 d e n, Patterson, 

 Frankland, Rupe, and many others; but definite laws which 

 might hold in al cases, have not yet been found. 



If no racemisation occurs during the reaction, we can suppose 

 that the new configuration in space will in general correspond 

 to that of the original antipode; however this is certainly not 

 always the case, as a change of place of the radicals round the 

 asymmetric atom during the reaction must indeed be considered 

 a strong possibility. Racemisation under such circumstances is 

 not seldom observed, especially if a phenyl-group be directly 

 linked to the asymmetric carbon-atom; so that the final 



reaction -product appears to be inactive. This sustains the view 

 that a certain "mobility" of the substitutes round the asym- 

 metric atom must be supposed, which under favorable circum- 

 stances may lead to a complete interchange of place between 

 the four radicals round the asymmetric central-atom, and to a 

 final re-arrangement in such a way as to reproduce the enantio- 

 morphous configuration of the original molecule, 



But even if no such change of configuration as is pictured 

 here, take place during the process, we are by no means sure 

 that the optical rotation of the obtained product will not have 

 the opposite algebraic sign to that of the original molecule. 

 Instances of this are well known: the salts of many optically 

 active acids show a rotation opposite to that of the acid itself, 

 and the same may be the case when organic optically active bases 

 are transformed into their salts by addition of ordinary in- 

 organic acids 



Thus the zinc-salt of dextrogyrate lactic acid 2 ) is laevogyratory, 



1) The theoretical development of the phenomenon of optical rotation is yet 

 far from being accomplished; see about this: G. H. Livens, Phil. Magaz. (6). 25. 

 817. (1913); 26. 362, 535. (1913); 27. 468, 994. (1914); 28, 756 (1914); M. Born, 

 Dynamik der Krystallgitter, (1915). 



2) E. Fischer and A. Skita, Zeits. f. physiol. Chemie 33. 190. (1901). 



