66 Biological Stains 



a8 NAPHTHOL green B C. I. NO. 5 



Synonyms: Naphthol green. Green PL. Acid green 0. 

 This dye probably has the formula: 



Some naphthol green, probably the second of the above two 

 dyes, has recently been employed by Volkmann and Strauss (1934) 

 as a component of a tissue stain, the other dyes used in combina- 

 tion with it being gentian violet and azocarmine G. Mollier 

 (1938) calls for it in a quadruple tissue stain, with orcein, iron- 

 hematoxylin, and azocarmine G. 



For the technic of MoUier's quadruple stain, see Staining Procedures*, p. IBs-T. 



2. NITRO DYES 



In this group the chromophore is -NO2. The chromophore is 

 of such a strongly acid character that the dyes of this group are 

 all acid dyes. 



bS picric acid C. I. NO. J 



Picric acid is formed by the action of nitric acid on phenol, 

 thus introducing three nitro groups: 



OH 



I 



02N_/\_N02 



Y 



NO2 



C6H3N3O7; Mol. Wt. 229.108 



(An acid dye; absorption maximum about 360 in alcohol) \ 

 Solubility at 26°C: in water 1.18%; in alcohol 8.96% 



*Ccftin and Darrow (1943-4). 



fWhen not otherwise specified, the absorption maximum is given for an aqueous 

 solution. 



