84 Biological Stains 



textile dye or in microscopic technic. It has been called for by 

 Ehrlich, however, in combination with pyronin and methyl green 

 or methylene blue to form a neutral dye. It is no longer on the 

 market, however. 



c81 AMARANTH C. I. NO. 1 84 



Synonyms: Naphthol red S, C or 0. Fast red. Bordeaux. 

 Bordeaux SF. Victoria rubin 0. Azo rubin. Wool red. 



N = N 

 HO \ 



NaSOs SOsNa 



NaSOs 



C2oHiiN20ioS3Na3; Mol. Wt. 604.475 



{An acid dye; absorption maximum about 525) 



Solubility at 26° C: in water 7.20%; in alcohol 0.01% 



Amaranth is not a commonly used stain, but is of considerable 

 importance as a food color. It has been used by Griesbach (1886) 

 for staining axis cylinders, by Chambers (1935) in staining cells in 

 tissue culture; also by Smith (1939) in color photomicrography. 



c85 METHYL RED C. I. NO. 2.11 



COOH CHa 



/ 

 /~\_N=N/ 



CH3 



C15H15N3O2; Mol. Wt. 269.294 



{A weakly acid dye; absorption maximum 530) 



This dye has rarely been used for staining, but has long been 

 employed as an indicator. Its useful range is from pH 4.4 to pH 

 6.0 in which it changes from red in acid solutions to yellow in 

 basic. Although still of value for this purpose it is coming to be 

 replaced by certain of the sulfonphthalein indicators such as brom 

 cresol green and chlor cresol green (see page 203), which are more 

 stable chemically and permit greater accuracy in reading. The 

 chief drawback to methyl red as an indicator is that it is easily 

 reduced with loss of color, and readings must be made very prompt- 



