Several attempts had already been made to obtain from the action of o-sulphobenzoic acid and resorcin a substance analogous to the fluoresceïn obtained by Baeyer[1] from phthalic anhydride and resorcin but while a strongly fluorescent substance was easily obtained, no definite compound could be separated from it. Thus Palmer obtained, by heating together the above named substances to 160°(?) a solid mass, part soluble in water and part insoluble as a dark brown amorphous powder. Both parts gave a strong fluorescence with alkalis. He was unable however to obtain the substance itself or any derivative in a crystalline form. [1] Annalin. No. 183. S. 1. No. 202. S. 36 & S. 153. Berichte. No. IV. S. 457. 555. 658. 662. ” ” VIII. S. 66. 146. The first experiments in this series gave the same negative results. The mixture of acid and resorcin was heated in a sulphuric acid both for several hours to 150°-170°, and as it showed no sign of solidification the temperature was raised to 200° and then to 235° where it was kept several hours longer. The black viscous mass obtained in this way became vitreous on cooling, and in all respects resembled that described by Palmer. This however is not the normal course of the reaction as shown later but is probably due to a decomposition of the normal product produced by too high heating. An experiment was made with the acid salt of ortho-sulphobenzoic acid. COOH ╱ C_{6}H_{4} ╲ SO_{2}OK, resorcin and H_{2}SO_{4} heating the mixture to 150°-170°. A solid black mass was obtained strongly fluorescent in alkaline solution and in all other respects like the substance obtained above. Preparation of Sulphonfluoresceïn. As the result of a number of experiments the following method of preparing and purifying the sulphonfluoresceïn was found to give the best results.