128 



Biological Stains 



l8 



NEUTRAL VIOLET 



CH3 



\ 



C. I. NO. 82.6 

 CH3 



N 



N. 



NH.HCl 



N 



CHj J CIIj 



\/-N=\y NH-\/ 



C22H25N6CI; Mol. Wt. 408.925 



{A weakly basic dye; absorption maximum 533) 



Solubility at 26°C: in water 3.27%; in alcohol 2.22% 



This dye is very similar in its properties to neutral red, except 

 that, due to its greater molecular weight, it is more bluish, giving 

 a violet instead of a red color. It can be used as an indicator, but 

 has been seldom used in histology. Unna (1921) however, has 

 used it in a dye mixture employed in the study of chromolysis. 



b. Safranins 



Quite a long series of azin dyes are known in which one of the 

 nitrogen atoms of the azin group is pentavalent and another ben- 

 zene ring is attached to it. This pentavalent nitrogen allows the 

 compounds to behave like ammonium bases; so with the amino 

 groups which are always present, the basic properties of these dyes 

 are very strong. The theoretical base of the simplest safranin 

 would have the formula: 



HaN 



This form of ammonium base does not actually exist, as the safra- 

 nin bases really occur in the form of anhydrides; but salts of these 

 ammonium bases are the commonly known dyes. The com- 

 mercial dyes are ordinarily chlorides. 



There are two groups of safranins : the benzo-safranins in which 

 the azin group unites two benzene rings; and the naphtho-safranins 

 in which it unites two naphthalene groups. The simplest safranin 

 is pheno-safranin, which is the chloride of the theoretical base just 

 given, namely: 



PHENO-SAFRANIN C. I. NO. 840 



Synonym : Safranin B extra. 



/\ N_/\ 



Lis 



H,N / \ NH, 



/\ CI 







C18H15N4CI; Mol. Wt. 322.789 



