158 Biological Stains 



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 crystal violet. This 

 dye, in fact, is coming to be the one member of this group in most 

 common use in biology. 



Spectrophotometric curves of typical samples of crystal violet 

 and methyl violet 2B are given in Fig. 21. Their great similarity 



o 400 460 520 



WAVELENGTH Tn>l 



Fig. 21. Spectral curves of two violet rosanilins: 

 1. Crystal violet. 2. Methyl violet 2B. 



is apparent, but the two products can be distinguished by accurate 

 measurement of the absorption maximum. 



Gentian violet. A poorly defined mixture of violet rosanilins is 

 well known to biologists under the name gentian violet. The name 

 is not used at present in the dye or textile industries. It apparently 

 applied originally to a certain mixture containing about half 

 dextrin and half dye, the dye being a methyl violet, that is a 

 mixture. of crystal violet with lower homologs of the same series. 

 The statement was formerly common in biological literature that 

 gentian violet is a mixture of crystal and methyl violet; but the 

 looseness of the statement is evident when it is realized that crystal 



