An alcoholic solution of the substance gave a black color with ammonia which became red on addition of more ammonia. Concentrated acids intensified the yellow color of the alcoholic solution. Fehling solution and ammoniacal silver nitrate were reduced by it. Potassium hydroxide added to an alcoholic solution gave at first a deep red color accompanied by a green fluorescence which disappeared, leaving a yellow liquid. With an excess of caustic potash, the red color returned and was permanent. These reactions are characteristic for fisetin.[24] Furthermore, fisetin should give protocatechuic acid and phloroglucinol by fusion with caustic potash under proper conditions.[25] The experiment was carried out as follows: 2 grams of fisetin were gently heated in a nickel crucible with 6 grams of caustic potash dissolved in 6 cc. water. An inflammable gas, apparently hydrogen, was evolved during the fusion. The pasty mass was dissolved in water, acidified with sulphuric acid, and filtered. The filtrate was shaken out with ether containing one-fourth its volume of alcohol. The ether was evaporated and the residue was extracted with warm water and filtered. Lead acetate was added to the filtrate to precipitate protocatechuic acid, while phloroglucinol remained in the filtrate from this precipitate. The lead precipitate was suspended in water, decomposed by hydrogen sulphide, filtered, and evaporated to obtain protocatechuic acid. That the substance obtained was protocatechuic acid was shown by the following characteristic tests: (1) It gave a greenish brown color with ferric chloride; on addition of one drop of a dilute solution of sodium carbonate, the color became dark blue; on adding more sodium carbonate the color became red. (2) A violet color was obtained when a solution of the acid was treated with a drop of sodium carbonate solution and then with a drop of ferrous sulphate. (3) It reduced ammoniacal silver nitrate. (4) It did not reduce Fehling solution. The filtrate supposed to contain phloroglucinol was treated with hydrogen sulphide to remove lead, filtered, and shaken with ether. The residue left on evaporating the ether was taken up in water. This solution gave the following reactions characteristic for phloroglucinol: (1) It reduced both silver nitrate and Fehling solution. (2) It colored pine wood moistened with hydrochloric acid red. (3) It gave a red color with vanillin and hydrochloric acid, and (4) A deeper red color with oil of cloves and hydrochloric acid, becoming purple on standing. (5) It gave a violet color with ferric chloride. The substance is then, without doubt, fisetin. The formula[26] of fisetin is supposed to be C_{15}H_{10}O_{6}. RHAMNOSE.