24 o SCIENCE PROGRESS 



but the change proceeds so slowly that after heating for forty- 

 two hours at 15 5° the proportions were still only 



^/-Acid meso-Ac\d /-Acid 



74 per cent. 18 per cent. 3 per cent. 



In the case of the salts, which undergo isomeric change 



when heated with an excess of alkali, the meso-compound is 



less stable than the racemic, the proportions for equilibrium 



being 



(^-Tartrate ;//r^-Tartrate /-Tartrate 



38 per cent. 24 per cent. 38 per cent. 



Camphoric Acid. /H 



r CH,-C< 



I \COOH 



C(CH 3 ) 2 



I /CH 3 

 CHj— C< 



\COOH 



which also contains two asymmetric carbon atoms, each linked 

 to a carboxyl group, =C.COOH, differs from tartaric acid in 

 that only one of them is inverted when the acid is heated with 

 water or with a mixture of acetic and hydrochloric acids, 

 df-camphoric acid being partially converted into /-isocamphoric 

 acid, but giving no trace of /-camphoric acid. This difference is 

 undoubtedly due to the fact that only one of the asymmetric 

 atoms is linked both to hydrogen and to carboxyl, the group 



v yCH 3 



}Q{ being incapable both of isomeric change and of 



x COOH 

 optical inversion. 



Gluconic Acid and the related acids of the sugar group 

 which contain four asymmetric carbon atoms linked to hydrogen 

 and hydroxyl, one terminal atom being also linked to carboxyl, 

 afford similar, but even more conclusive evidence of the 

 necessity of a mechanism for bringing about optical inversion, 

 since when the acids are heated with pyridine or with quinoline 



at 130-150 01 all the /C\ groups retain their original 



/ X OH 

 asymmetry with the exception of the terminal atom which carries 

 the — COOH group and which alone becomes inverted. 



1 Fischer, Ber. 1894, 27, 3193. 



