76 Biological Stains 



c«8 NITRAZINE 



Synonyms : Nitrazine yellow. Delta dye indicator. 



NO. OH 



I 



/\ N_N 



NO. NaSOj SO3 Na 



Ci6H8N40iiS2Na2; Mol. Wt. 542.370 



{An acid dye) 



This dye has recently been proposed as an indicator, having a 

 pH range of 6.0 to 7.2. Its acid color is bright yellow, from which 

 it passes thru gray-green into its alkaline color, bright blue.This 

 indicator can be used in the form of test strips, like litmus paper. 

 It is more sensitive than litmus, however, and shows greater color 

 contrast. Lillie (1940) finds it can replace xylidine ponceau in the 

 Masson (1929) trichrome stain. 



For technic of Masson trichrome stain, Lillie modification, see Staining Pro- 

 cedures, p. IB3-I8. 



cSl SUDAN II C. I. NO. 73 



Synonyms: Oil scarlet. Fast oil orange II. Red B. Fat ponceau. 



Orange RR. 



C18H16N2O; Mol. Wt. 276.324 



{An acid dye; absorption maxima in alcohol: 531. 5y 4.94-5) 



Solubility at 26°C: in water nil; in alcohol 0.39% 



In this dye the hydroxyl group is in the ortho position with re- 

 spect to the azo group. As explained above (p. 69), such com- 

 pounds show a tendency toward intramolecular rearrangement so 

 that the hydrogen atom detaches itself from the hydroxyl group 

 and becomes fixed to the neighboring nitrogen. Such a com- 

 pound is neither acid nor basic and, not being able to form salts, is 

 not an ordinary dye, but is fat soluble and has the power of color- 

 ing fat. Therefore, this compound, together with the following 

 and several others of similar structure described below, are fat 

 stains. 



This fat stain has frequently been confused with oil red O be- 

 cause both are mistakenly given in the Colour Index as synonyms. 



