INVESTIGATION OF AMERICAN STAINS 141 



GENTIAN VIOLET 



The term gentian violet is at present very indefinitely used. 

 Grubler apparently originated it, applying it to a certain mixture 

 of dyes all closely related chemically and having similar staining 

 properties. These dyes belong to the pararosanilin series. The 

 pararosanilin base is considered to have the formula: 



/CCH4NH2 



In this formula it will be noticed that there are six hydrogen 

 atoms attached to the three amino-nitrogen atoms. These six 

 hydrogen atoms may each be replaced by a methyl group (CH3), 

 and ethyl group (dRi) or even by a benzyl group (CeHs). The 

 comi^ounds of most importance in gentian violet are those with 

 four, five and six methyl groups respectively, known as: 



tetramethyl-pararosanilin 

 pentamethyl-pararosanilin 

 hexamethyl-pararosanilin 



In these three compounds, the greater number of methyl 

 groups present the deeper is the shade of violet. Thus the tetra- 

 methyl compound is a reddish violet while the hexamethyl 

 compound is a bluish violet. The introduction of a benzyl 

 group tends to darken the shade still further. The tetra- and 

 pentamethyl compounds are seldom prepared in a pure state, but 

 the hexamethyl compound, mider the name of crystal violet, is 

 readily obtainable in fairlj' pure form. Criibler's gentian 

 violet, besides these compounds, is supposed to have contained 

 other rosanilins, but these three methylated pararosaniUns 

 were the most important constituents. American gentian violets 

 are sometimes pure crystal violets, sometimes some other dj^e 

 of this series, and sometimes various mixtures of the above 

 mentioned dyes. The term gentian violet is not used by the 

 dealers in textile dyes nor by their dye chemists. This stain is 

 ordered only by the biologist, and hence it is furnished only 

 by biological supply houses and some dye manufacturers that 

 specially cater to the biologist. 



