. Biological stains; a handbook on the nature and uses of the dyes employed in the biological laboratory. Stains and staining (Microscopy); Stains and Staining; Dyes. 184 Biological Stains 3. FLUORAN DERIVATIVES Fluoran is not a dye, but is a very important compound in dye chemistry. It is a derivative of phthalic anhj'^dride, 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. The fluoran dyes are derivatives of this by the introduction of hydroxyl groups into two of the benzene rings at the p
. Biological stains; a handbook on the nature and uses of the dyes employed in the biological laboratory. Stains and staining (Microscopy); Stains and Staining; Dyes. 184 Biological Stains 3. FLUORAN DERIVATIVES Fluoran is not a dye, but is a very important compound in dye chemistry. It is a derivative of phthalic anhj'^dride, 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. The fluoran 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. The dyes of this group are also, and equally correctly, spoken of as the fluorescein derivatives, fluorescein being, as will be seen on p. 186, a salt of di-hydroxy- fluoran. Sometimes, moreover, the fluorescein dyes are referred to as the eosins. This term to cover the whole group is hardly justified, as it is better to call eosins only the dyes definitely so named below. The fluorescein dyes are all similar in their action, but with certain decided differences. In order for the reader to obtain a real understanding of these stains and their behavior, a general discussion of the whole group is necessary. The dyes in this group most important to the biologist are: eosin Y, C. I. No. 768 (also called eosin yellowish or eosin water soluble); ethyl eosin, C. I. No. 770 (also called eosin alcohol soluble); eosin B, C. I. No. 771 (a
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