12 Robinson, The Conjugation of Partial Valencies 



This expression as a vehicle for the explanation of the 

 behaviour of the compound has grave defects, and, since the 

 interpretation of the properties of the carbonyl group is very 

 much a matter of opinion and relations of colour to structure 

 still more so, the criticism of the formula may be confined to 

 its failure to indicate the non-basic character of indigotin and 

 the anomaly of the non-existence of cis-trans modifications. 

 There seems to be no reason why the isomeride, 



has never been isolated. All these and other objections are 

 completely met by regarding indigotin as a true indole deri- 

 vative. The series of formulas now suggested are : — 



C-OH 



Indigo White. 



Indigotin. 



