70 Biological Stains 



oil and is able to color it by an apparently physical process. Hence 

 the azo-ortho-phenols, or azo-beta-naphthols, like Sudan III and 

 Sudon IV, 



are important fat staining dyes. 



B25 NUCLEAR FAST RED SALT R 



OCH3 



/\_N = N— ONa 



N02-\/ 

 C7H4N304Na; Mol. Wt. 217.123 



This compound is not a dye, but is mentioned here because it 

 forms an azo dye when combined with phenols and certain phenolic 

 derivatives, and is used as a histochemical reagent, producing a 

 bright red in the tissue in the presence of such compounds. It is 

 best known to the biologist by the German name "Kernechtrotsalz 

 B" under which it has been sold by a stain company in that 

 country. Clara (1935) describes the use of such compounds for 

 this purpose. Jacobson (1939) similarly employs it in the study 

 of argentaflBne cells. 



The compound is really a diazonium salt like those described in 

 Chapter X among the histochemical reagents. It is a diazo salt of 

 5-nitro-2-amino methoxybenzene closelv related to National Ani- 

 line's fast red salt B (see p. 234). 



a. MoNO-Azo Dyes 



Gl FAST YELLOW C. I. NO. 1 6 



{Echt Gelh) 

 Synonyms: Fast yelloiv FY, G, S, BGy etc. Acid yelloui. 



N = N SOsNa 



NaSOa NH2 



Ci2H9N306S2Na2; Mol. Wt. 401.330 

 {An acid dye; absorption maximum about It-90 in acid solution) 

 Solubility at 26° C: in water 18.^0%; in alcohol 0.24%. 



