ISOMERIC CHANGE 637 



It is abundantly clear from these observations that the main 

 applications of Laar's theory have proved to be incorrect when 

 examined in the light of subsequent experience. A secondary 

 application, referred to incidentally in his earlier paper (p. 656), 

 remains to be dealt with. The only case cited is that of quinone, 

 which may be formulated as 



O = C S H, = or O - C 6 H 4 - O 



and, according to the theory of tautomerism, should be in a con- 

 stant state of vibration or oscillation between these two forms. 

 The benzene compounds discussed by Kekule form another 

 instance in which a constant motion of the bonds is postulated, 

 although the atoms are supposed to retain the same relative 

 arrangement throughout. Laar's suggestion has recently been 

 revived by Baly (Trans. 1906, 89, 498) under the name of " isor- 

 ropesis" in connection with certain optical phenomena which 

 it is proposed to discuss in a subsequent article. At present, 

 therefore, it will suffice to say that the existence of isomeric 

 forms of quinone is a matter of pure speculation, unsupported 

 by any concrete evidence whatever, and that, until some such 

 support is forthcoming, the whole conception of " tautomerism " 

 must be regarded as an ingenious and fascinating hypothesis, 

 but nevertheless mere fiction. 



