The role which the organic* acids play in plant metabolism is not well understood. The work of Pucher, Vickery, and Wakeman (4, 5, 6, 7, 8, 9) on tobacco and other plant materials has opened the way for many investigations on total organic acids and on the various individual organic acids such as malic, oxalic, pyruvic, citric, and succinic. In our investigations on the acid content of apples the need was felt for a rapid and reliable method for the estimation of mixtures of succinic and malic acid. While the existing methods for the determination of the total organic acid are relatively simple, the determination of succinic acid as succinyl p-toluide was not entirely satisfactory because of the difficulty of the processing of a large number of samples through all the steps of the method. The fluorometric spot test described by Feigl (1) for the estimation of acids seemed promising for development into a rapid quantitative method. In this method the acids are heated with resorcinol and concentrated sulf uric acid and upon addition of alkali the fluorescence in ultraviolet light is measured. Feigl (1) states that dicarboxylic acids with the carboxyl groups in the 1,2 or 1,4 positions or their derivatives, such as esters, anhydrides, or imides, form dyes of the fluorescein type on melting with resorcinol, ' ' and these give a vivid greenish-yellow fluorescence in alkaline solutions by daylight and a greenish-blue fluorescence in ultraviolet light. Under the conditions described by Feigl, malic acid forms semi-aldehydes of malonic acid or its homologues which condense with resorcinol to umbellif erone or its homologues, and these fluoresce a brilliant blue in alkaline solution under the mercury vapor lamp. It was found, however, that this solution is not stable in an alkaline reaction and the intensity of the fluorescence fades upon standing in aqueous solution at room temperature. Pringsheim (3) states that in general any photoluminescent substance has an absorption band in the spectral region immediately adjoining the shortwave limit of the luminescence band and even somewhat overlapping it. Red, therefore, is excited by orange light, yellow, by green, green, by blue, and violet by ultraviolet. 1 Published with the approval of the Director of the Michigan Agricultural Experiment Station as journal article no. 757 n.s. 2 Present address : John Bean, Division Food Machinery Corp., Lansing, Mich. 443