STAINING, PRACTICAL AND THEORETICAL 



Chromophore : 



AZIN GROUP 



\ / 



C— N=C 



C— N=C 

 / \ 



These dyes also contain a quinonoid ring structure to complete 

 the chromophore. Because of this configuration, the azins belong 

 to the broader class of quinonoid dyes. The latter group also 

 includes the indamines, the indophenols, the indulins, the 

 oxazins, the thiazins, the triarylmethanes, etc. 



Only about twelve azin dyes are used as microscopical stains. 

 Of these, two are acid dyes; the rest are basic. Some examples of 

 azin dyes are given below: 



AZOCARMINE B 



Michronie No. 319. Molecular weight 682. An acid dye, 

 pH 675*. Solubility at 15° C: water 2%, absolute alcohol o-o^%. 



SOsNa 



SOsNa 



NEUTRAL RED 



Michrome No. 226. Molecular weight 289. A basic dye, pH 5 • i *. 

 Solubility at 15° C: water 4%, absolute alcohol i-8%. 



(H3C)2N- 



'— N 



I 

 H 



-CH3 

 -NH2 



+ 



ci- 



* 1% in neutral distilled water; see pages 17 and 29. 



40 



