Quinone-imine Dyes 129 



Moore (1933) has called for phenosafranin in staining colonics of 

 bacteria and fungi. The commercial safranins are ordinarily 

 methyl or ethyl substitution products of this; or occasionally 

 phenyl substitution products. The one of greatest value to the 

 biologist is generally called safranin O. 



L20 SAFRANIN O C. I. NO. 84 1 



Synonyms : Safranin Y or A. Gossypimine. Cotton red. 



SHghtly different shades: Safranin AG, T, MP, and G. (Although 

 all included in C. I. No. 841 they are different from the grade 

 here described.) 



{A basic dye; absorption maximum about 530) 

 Solubility at 26° C: in water 5.4.5%; in alcohol 3.41% 



The common safranins of commerce, under various shade 

 designations, are mixtures of di-methyl and tri-methyl pheno- 



C2oHi«N4Cl; Mol. Wt. 350.841 C21H21N4CI; Mol. Wt. 364.867 



The shade differs according to the proportion of these compounds 

 present, the red being deeper according to the proportion of the 

 tri-methyl compound in the mixture. The type safranin O, which 

 proves best for ordinary biological purposes, can be defined as 

 having its absorption maximum at 530m /x. 



A spectral curve of safranin O is given in Fig. 16. 



Safranin has always been a problem, because of its variability, 

 especially in cytological work where it is often employed together 

 with another basic dye, and a delicate balance between the two 

 stains is necessary. The reason for this variation has been a 

 puzzle ever since the Commission has begun its investigations of 

 this dye. The question is not yet answered. It is realized at 

 present, however, that there are samples that stain too blue, and 

 others that stain too yellow, although this difference does not cor- 

 relate with dye content nor with any chemical properties of the 

 dye yet investigated. Strangest to say, there is no difference be- 

 tween any of these types of safranin that can be recognized by the 

 spectrophotometer. Under such circumstances, no truly scientific 

 method of standardizing the stain has been|devised. An empirical 

 method is in effect, however, which results in the present product 



