This theory explains the fluorescence of anthranilic acid (o-aminobenzoic acid), by regarding the aniline residue as the luminophore, and the carboxyl group as the fluorogen, since, apparently, the introduction of the latter into the non-fluorescent aniline molecule involves the production of a fluorescent substance.
Although the theories of Meyer and Hewitt do not explain (in their present form) the behaviour of anthranilic acid, yet Hewitt has shown that his theory goes far to explain the fluorescence of substances in which a double symmetrical tautomerism is possible.
Ortho-amino-benzoic acid, C 6 H 4 NH 2 000H (anthranilic acid), is closely related to indigo.
Bromine and potash give anthranilic acid, C 6 H 4 (NH 2) (CO 2 H).