There is considerable confusion in the nomenclature of these 

 dyes, as the names employed may be used in a strict chemical sense 

 or in a looser sense in practice. Chemically there are two rosolic 

 acids, which are related just as are rosanilin and pararosanilin. 

 Pararosolic acid differs from pararosanilin, only in having hydroxyl 

 groups in place of the amino groups : 



H.N /~\ /^ NH. HO /^\ /—\ OH 



OH 



.NH^ 

 HO 



Pararosanilin carbinol 



leuco-pararosolic acid 



Rosolic acid, on the other hand, is a mono-methyl derivative, and 

 bears the same relation to rosanilin : 



H.N 



CH, 



NH. 



HO 



OH 



c / c 



/ \/~\_NH2 CH 



HO \_/ 



Rosanilin carbinol leuco-rosolic acid 



Now the dye to which the name rosolic acid or aurin is generally 

 given in practice is a mixture consisting of both rosolic acid and 

 pararosolic acid together with other closely related compounds. 

 This dye is: 



AURIN OR ROSOLIC ACID C. I. NO. 724 



A mixture of rosolic acid and pararosolic acid, with oxidized and 

 methylated derivatives of the latter. This product is of consider- 

 able use as an indicator. 



Corallin yellow is the name given to its sodium salt. 



No other dyes of this group have biological use. Two others 

 perhaps deserve mention: 



CORALLIN RED C. I. NO. 726 



Synonym: Aurin R. 



Apparently a compound dye, the pararosanilin salt of pararosolic 

 acid. 



CHROM VIOLET 



A carboxyl derivative of pararosolic acid : 



COONa 



0_/~X— 



C. I. NO. 727 



/ 

 COONa 



COONa 



74 



