This shows their close relation to the next group of dyes, namely 

 the fluorane derivatives, which as will be seen are also prepared 

 from phthalic anhydride. In fact these two groups of dyes, acid 

 and basic respectively, are related in exactly the same way as the 

 rosolic acids and the rosanilins, the one group having hydroxyl 

 radicals where the other has amino groups. 



3. FLUORANE DERIVATIVES 



Fluorane is not a dye, but is a very important compound in dye 



chemistry. It is a derivative of phthalic anhydride, and contains 



a xanthene ring (five C atoms and one O atom) as well as a lactone 



ring (four C atoms and one O atom) besides three benzene rings; 



thus : 



O 



c 



I "CO 



The fluorane dyes are derivatives of this by the introduction of 

 hydroxyl groups into two of the benzene rings at the para position 

 to the central carbon atom and the further introduction of halogen 

 atoms at various positions in all three benzene rings. 



It proves convenient here to class these compounds with the 

 xanthene dyes. They may, however, be equally well considered 

 tri-phenyl-methane dyes, as can be seen by a glance at the formula 

 of any of them; in fact they are generally so considered by the 

 chemists. To the biologist they stand in a distinctly different class 

 from the tri-phenyl-methanes ; and for that reason are treated here 

 instead of in the preceding chapter. 



FLUORESCEIN C. I. NO. 7 66 



Synonym: Uranin. 



This is the simplest of the fluorane dyes, and is the mother sub- 

 stance of the eosins. The composition of its sodium salt is: 



NaO 



O /\-0 



'C= 



COONa 



\/ 



(An acid dye; absorption maximum about 4-90.) 



78 



