This dye is rarely used as a biological stain, but is called for by 

 Schaffer for staining sections of bone, and by Unna in certain stain 

 mixtures used in studying the phenomenon called by him chro- 

 molysis. 



METHYL ORANGE C. I. NO. 1 42 



Synomyms: Orange III, Helianthin, Gold orange, Trapaeolin D. 



N = N CHj 



NaS03_| I I i_N 



\/ \/ \ 



CHj 



{A weakly acid dye; absorption maximum about 506 in 



acid solution) 



This dye has little use as a stain, but is widely employed as an 

 indicator, as it is red in acid, and orange in alkaline solutions. Its 

 chief value as an indicator is that it is sensitive to mineral acids 

 without being affected by carbonates or most organic acids. It has 

 been used by Bergonzini in the place of orange G in the Ehrlich- 

 Biondi stain; and byEbbinghaus for staining keratin in sections of 

 skin. 



ORANGE IV. C. I. NO. 1 43 



Synonyms: Orange N. Acid yellow D. Tropaeolin 00. 



NaS03 

 {An acid dye; absorption maximum about 521 in acid solution) 



The onlv biological use of this dve seems to be occasionally as 

 an indicator. 



ORANGE I. Ot^. no. 150 



Synonyms: Naphthol orange. Tropaeolin G. or 000 No. 1. 



N = N 



OH 



{An acid dye; absorption maximum about ^76) 



This is another dye which is turned red by excess of alkali and 

 has therefore some use as an indicator. 



36 



