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.
It does not melt at 250° but if held at a lower temperature for a long time becomes red undergoing some decomposition. If quickly heated somewhat above 300° it melts to a deep red liquid and then solidifies. If the mass is treated with water it partly dissolves leaving a dark brown flocculent precipitate which dissolves on the addition of an alkali, the solution having an intense fluorescence, nearly if not quite equaling that of fluoresceïn. This change produced by heating was not further studied.
The crystals are very thin blades, apparently monoclinic, showing the clinopinacoid αΡὰ and a very narrow prism αΡ and clinodome Ρὰ. The angle β = 75° and the extinction angle against the ϲ axis = 20°. The axial ratio could not be accurately determined.
Salts of sulphonfluoresceïn.
The influence of the SO2 group is shown by the fact that the substance acts as an acid decomposing carbonates and forming salts which is not the case with fluoresceïn.
Barium salt.
The substance was boiled with an excess of carefully purified BaCO3 for two hours. The filtrate from the BaCO3 evaporated to a small volume deposited yellow crystals resembling the original substance but in shorter and thicker prisms. These were twice recrystallized and had then a light straw yellow color.
A determination of the Ba gave the following results. The salt was dried in the air.
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