may be recrystallized from ethylene dichloride (C2H4CI2) in which 

 it forms a deep carmine red solution. Although insoluble in water 

 when pure, methylene violet is soluble when mixed with methylene 

 blue or with the azures. It plays an important part in the nuclear 

 and granule staining of the polychrome methylene blue stains. A 

 definite quantity of this dye is employed in the tetrachrome blood 

 stain of MacNeal. 



Methylene violet (Bernthsen 1885) is not a textile dye and must 

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

 No. 842. 



CH3 



CH, 



METHYLENE GREEN 

 NO. 



C. I. NO. 924 



CH3 



N_/\_S _/\ = N-CH, 



CI 



-N=\/ 

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



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. 



TOLUIDINE BLUE O C. I. NO. 925 



Synonym: Methylene blue 0. 



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

 structure, and even more closely to methylene azure A : 



CH3 



\ 



N 



CH, 



"N= 



,NHaCl 

 CH. 



{A basic dye; absorption maximum about 635.) 



Toluidine blue is not ordinarily used for textile dyeing, but is more 

 easily prepared than thionin — a fact of considerable importance, 

 as it has properties very much like the latter. It proves, in fact, 

 that it can be substituted in many ways for thionin, as for example 

 in staining frozen sections of fresh tissue. It is quite a useful stain, 

 being an important ingredient of Pappenheim's panchrome stain 

 for tissues and blood, and also the main constituent of the Albert 

 stain, which is at present replacing methylene blue in the diagnosis 

 of diphtheria. 



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