Quinone-imine Dyes 



115 



For formula and technic of MacNeal's Tetrachrome Stain, see Staining Pro- 

 cedures, p. ID 3-5. 



For use as counterstain to alizarin red S for calcium deposits, see Id. p. ID3-I6. 



Methylene violet (Bernthsen 18$5) is not a textile dye and must 

 not be confused with methylene violet RRA or 3RA, which is 

 C. I. No. 842. 



J20 



CH3 



CHa 



\ 



I 



/ 



N 



METHYLENE GREEN 



NO2 CHa 



S_/\=N— CHa 

 CI 



C. I. NO. 914 



'N= 



./ 



C16H17N4O2SCI; Mol. Wt. 364.845 



{A basic dye; absorption maxima at about 660, 607.) 



(Solubility at 26° C: in water 146%; in alcohol 0.12%) 



This dye is a mono-nitro methylene blue, obtained by the action 

 of nitrous acid on methylene blue. The formula is probably as 

 given above, but the exact position of the nitro group is uncertain. 



It is occasionally used as a substitute for methyl green, especially 

 by botanists in the case of wood and fixed chromatin, and gives 

 good results in combination with eosin. It has also been employed 

 by Lison (1938) as a vital stain for insects. 



J25 



TOLUIDINE BLUE O 



C. I. NO. 915 



Synonym : Methylene blue T 50 or T extra. 



This dye is closely related to thionin and to methylene blue in 

 structure, and even more closely to azure A: 



CHa 



CHa 



\ 



I 



/ 



N_/\_ S_/X=NH2C1 



CHa 



C15H16N3SCI; Mol. Wt. 305.819 



{A basic dye; absorption maximum 620-622.) 



Solubility at 26°C: in water 3.82%); in alcohol 0.57%o 



In practice it proves difficult to distinguish this dye from azure A 

 by spectrophotometric tests. This is particularly true because a 

 shift in the absorption band of toluidine blue O sometimes occurs in 



