{Basic dyes; absorption maxima: 583-58 J^ in 90% alcohol.) 



In the case of these compounds, as in the case of other series of 

 homologs differing in extent of methylation, the shade is deepened 

 by the introduction of each methyl group. Hence the various 

 mixtures known to the trade as methyl violet vary from reddish to 

 bluish violets according to the relative amounts of the more and 

 less completely methylated compounds present in the mixture. 

 This is the significance of the various shade designations listed 

 above, R's indicating the reddish shades, and B's the bluish shades. 

 Of these various shades the bluer ones seem to be best for biological 

 purposes, methyl violet 2B having been found satisfactory for 

 practically all purposes for which methyl or gentian violet is 

 ordinarily called for. This indicates that the biologist requires the 

 higher homologs in this group. Now the most completely methy- 

 lated methyl violet is the hexa-methyl compound, which is easily 

 obtained pure and is known to the trade as crj^stal violet. This 

 dye, therefore, appeared very interesting to the Commission and 

 has been given considerable investigation. 



CRYSTAL VIOLET C. I. NO. 68 1 



Synonyms: Violet C, G, or 7B. Hexamethyl violet. Methyl violet 



lOB. Gentian violet. 



(A basic dye; absorption maximum about 591.) 



This dye is hexa-methyl-pararosanilin, whose formula is given 

 above as one of the components of methyl violet. 



The Commission has made as careful an investigation of this 

 dye as of any other and has become very enthusiastic over it. 

 Methyl or gentian violet is of chief value to the biologist as a 

 nuclear or chromatin stain, having many histological and cyto- 

 logical applications, the one for which it is most commonly used at 

 present being the Flemming triple stain in which it is employed 

 with orange G and safranin — a technic which gives a very high 

 degree of differentiation. It is also used for staining amyloid in 

 frozen sections of fresh and fixed tissue, and for staining the plate- 

 lets in blood; while it is much used by the Weigert technic for stain- 



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