These analyses show with but little doubt that the substance has the composition indicated above i.e. C_{19}H_{12}O_{6}S+2H_{2}O. The reaction therefore which takes place between ortho-sulpho benzoic acid and resorcin from its analogy to that taking place between phthalic anhydride and resorcin may be represented thus, as shown by Baeyer in his second paper (Ann. 202. S. 43) Representing the formation of the anhydride as the first action. COOH CO ╱ ╱ ╲ C_{6}H_{4} = C_{6}H_{4} O + H_{2}O \ ╲ ╱ SO_{2}OH(o) SO_{2} and the action of resorcin on this anhydride thus. CO OH ╱ ╲ ╱ C_{6}H_{4} O + 2C_{6}H_{4} ╲ ╱ ╲ SO_{2} OH (m) O ╱ ╲ (HO)H_{4}C_{6} C_{6}H_{4}(OH) ╲ ╱ = C + 2H_{2}O ╱ ╲ C_{6}H_{4} O ╲ ╱ SO_{2} The substance thus formed would naturally receive the name Sulphonfluoresceïn from its analogy with Fluoresceïn. ┌─ │ OH │ ╱ │ C_{6}H_{3} │ ╲ │ O │ ╱ C ─┤ C_{6}H_{3} │ ╲ │ OH │ │ C_{6}H_{4}SO_{2} │ ╱ │ O └─ Sulphonfluoresceïn. ┌─ │ OH │ ╱ │ C_{6}H_{3} │ ╲ │ O │ ╱ C ─┤ C_{6}H_{3} │ ╲ │ OH │ │ C_{6}H_{4}CO │ ╱ │ O └─ Fluoresceïn. Properties of S.fluoresceïn. This compound shows a marked similarity to the fluoresceïn described by Baeyer as would naturally be expected from its great similarity of composition and constitution, but it also shows decided differences which may be attributed to the replacement of CO by SO_{2}. Dissolved in water it shows a weak green fluorescence which in alkaline solution becomes much deeper but not by any means so strong as that of fluoresceïn. The dilute alkaline solution by transmitted light is almost perfectly colorless and by reflected light a clear green. Unlike fluoresceïn it is extremely soluble in water, about one part in two or three of hot and five or six of cold water. It is also soluble in absolute alcohol forming a yellow solution with weak fluorescence. It is soluble with difficulty in ether but when in solution is deposited only on evaporating to a small volume.