ON ABSORPTION SPECTRA AND CHEMICAL CONSTITUTION. 

 QUINONE DIOHLOBIMIDE — oontiniied. 



119 



Lastly, it may be remarked that in the report for 1899, p. 345, there are 

 some brief observations on the origin of colour and on fluorescence, which 

 give a physical explanation of the cause of colour in a hydrocarbon ; 

 the observations are illustrated by reference to the constitution of triphenyl 

 methane, a compound without any visible colour ; of anthracene, which 

 in the state of greatest purity is faintly coloured ; and to bi-diphenylene 

 ethylene, which is strongly coloured red. It would be difficult to account 

 for these coloured substances by assuming a particular structure for 

 quinone, and further assuming that all coloured substances and dyes had 

 a structure similar to that of quinone. In connection with this subject 

 reference may be made to some recent work of v. Baeyer and Villiger on 

 dibenzylidene acetone and triphenyl methane.^ They refer to the constitu- 

 tion of colourless substances which form highly coloured salts, and term the 

 phenomenon halochromism. The colour is not due to a quinonoid constitution 



<0 



CgH^ 



Ho 



for it is even shared by triphenyl methane ; and, furthermore, these acetone 

 derivatives are constituted in an essentially different manner from that of 

 quinone and of the dyes and coloured substances formulated upon a 

 similar typical structure. 



' Ber., 1902, 35, 1189-1201; also C. Sac. J. Abstr., 1902, vol. i. pp. 112 and 380, 

 June 1902. 



