The following investigation on the absorption of fluorescein was undertaken in the course of our study of triphenylmethane derivatives.3 The absorption of fluorescein has been studied extensively in the past but the recorded data show wide variations. In the earlier work,4 only solutions of alkali salts of fluorescein were employed. Meyer and Fischer5 prepared a violet solution of fluorescein by boiling it with a concentrated solution of alkali. They called attention to the similarity of its absorption spectrum with that of phenolphthalein in dilute alkaline solution. Medhi and Watson6 and Howe7 compared the absorption of neutral and alkaline solutions of fluorescein in the visible and ultraviolet regions, respectively. Howe also reported on the absorption of fluoran in neutral and alkaline alcoholic solutions. Moir8 studied the visible absorption of fluorescein in coned, sulfuric acid solution. Other reports on the absorption in the visible region were made by Nichols and Merritt,9 Formánek and Knop10 and Holmes.11The lack of concordant results can be ascribed to two causes: (1) using impure materials, such as commercial preparations or extracts made directly from the fusion mixture; (2) neglecting to mention concentrations, both of fluorescein and alkali in the case of alkaline solutions, for 1 The assistance of a grant made to the first two authors from the Heckscher Research Foundation of Cornell University which enabled us to make the measurements described in this report is gratefully acknowledged.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.