502 SCIENCE PROGRESS. 



ment of the preceding one. In nature plants form from their 

 inactive food (carbonic acid, water, ammonia, etc.) all kinds 

 of active substances as terpenes, carbohydrates, alkaloids ; 

 and in the animal organism it has been shown that inactive 

 bromobenzene is converted into active bromphenylmer- 

 capturic acid (Baumann and Preusse, Ztsckr. f. physiol. 

 Chem. v., 309, Ber. xv., 1 73 1 ). In the laboratory, micro- 

 organisms are employed. Thus Le Bel obtained right- 

 handed amyl-alcohol, CH 3 C 2 H 5 CHCH 2 OH, by means of 

 penicillium, and Tutton [Chem. Soc. J., 1891, 233) formed 

 left-handed glyceric acid, CH 2 OHC HOHCOOH, by means 

 of bacillus ethaceticus. 



The disadvantage of this method is that one isomer is 

 lost. 



III. Spontaneous conversion. On crystallising a solu- 

 tion of sodium ammonium racemate, Pasteur found the 

 two tartrates separate. This result depends on the tem- 

 perature employed. The method has been recently used 

 by Zelinsky {Ber. d. Chem. Ges., xxiv., 4014). 



By the employment of one or other of these three 

 methods, activity has been demonstrated in almost all the 

 molecules containing an asymmetric carbon atom, which 

 have been tested. There are still a few exceptions 

 outstanding, in particular certain chlorine and bromine 

 derivatives of succinic and acetic acids. The explanation 

 of these cases is, that when halogens are united with the 

 asymmetric carbon atom racemisation very readily results. 

 The stability of the right- and left-handed isomers is slight ; 

 the one may be converted into the other by heat and even 

 by catalytic action, as when tartaric is converted into racemic 

 acid by oxide of iron or by alumina. Now when isomerisa- 

 tion takes place inactivity must result. For owing to the 

 complete mechanical symmetry of the two systems of like 

 atoms, the tendency to conversion will be the same in both, 

 and there will always be more converted of that isomer 

 which is in excess until equal quantities of both are present 

 (Van't Hoff, Atome im Raume, 1894, p. 32). 



When, therefore, we find bromo-succinic acid, made from 

 active malic acid, to be inactive, while chloro-succinic acid 



