I 



extensively used by plant pathologists in studying sections of 

 tissue infected by fungi. The dye is also used in preparing certain 

 light filters used in photomicrography. 



AURANTIA C. I. NO. 12 



Synonym: Imperial yellow. 



This dye is the ammonium salt of hexanitro-diphenylamine. 



NO, NO, 



\ 

 O.N_/— \_N_ 



\_/ 



/ / 



NO, NO, 



(An acid dye; absorption maximum about J^25) 



It is obsolete as a textile dye and is almost unknown as a biological 

 stain. It is called for, however, in combination with toluidine blue 

 and acid fuchsin in the Champy-Kull technic for demonstrating 

 certain cell constituents (mitochondria, etc.) 



2. THE AZO GROUP 



The azo dyes are characterized by the chromophore — X = X — 

 joining benzene or naphthalene rings, thus: 



N = N 



\/\ 



It is possible for the azo group to occur more than once in a mole- 

 cule, forming the disazo dyes, thus: 



N = N 



N = N 



The azo chromophore is distinctly basic; but not sufficiently so to 

 make the dves basic when thev contain hvdroxvl radicals. Those 

 containing amidogen radicals are, of course, pronouncedly basic. 

 The position of the hydroxyl or amidogen group on a benzene 

 ring in relation to the azo groHip is important. Ordinarily they are 

 in the para position to each other, thus: 



N = N 



\/ \/\ 



OH 



The ortho position is next frequently assumed; rarely the meta 

 position. When the hydroxyl group assumes the ortho position the 

 character of the compound is quite distinct from that of the para 



33 



