STAINING 



125 



than to place it in one or another of the above-mentioned chemical 

 groups. 



234. The General Nature of Dyes. The artificial dyes are all 

 derivatives of benzene which has the structural formula 



C 



c c 



\/ 



c 



and is ordinarily indicated in more complex formulae as a mere 



hexagon thus 



There is a series of derivatives of 



benzene which is also of importance in the constitution of dyes, 



NH, 



among which is anilin 



Because so many of the first 



artificial dyes produced were derived from anilin, the term " anilin 

 dyes " is often used to apply to all these products, although anilin 

 does not enter into the formation of all the synthetic dyes at 

 present manufactured. Other simple derivatives of benzene 

 from which many dyes are derived are the following : — • 



CH, 



CH., 



CH, 



CH, 



NH., 



Toluene 



Xylene 

 (ortho) 



Toluidine 

 (ortho) 



Naphthalene 



The last of these, as will be readily understood, is a condensation 

 of two benzene rings sharing two carbon atoms and having only 

 eight hydrogen atoms between them. 



Another simple derivative of benzene which has a very intimate 

 relation to many of the dyes is quinonc. This compound is a 

 dioxide of benzene ; and to account for the replacement of two 

 monovalent hydrogen atoms by two bivalent oxygen atoms, it is 

 necessary to assume a rearrangement of the internal bonds of the 



