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.

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.

resorcin and H₂SO₄ 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.

The free acid is mixed with resorcin in the proportion of 1 part acid to 1.2 parts resorcin, or a slight excess over two molecules of the latter to one of the former. The mixture is placed in a deep vessel, a test tube or beaker, which is placed in a sulphuric acid bath, a thermometer being suspended in the mixture. The bath is heated and at about 100° the resorcin melts and the acid slowly dissolves in the liquid. No action appears to take place till the temperature reaches 175° where water begins to be given off and the liquid slowly assumes a darker color. White crystals of resorcin collect on the sides of the vessel. After the heating has been continued for about seven hours at 178°-185° the liquid has a clear deep red color but shows no signs of becoming viscous. At length lustrous yellow crystalline plates appear in the liquid and soon the whole mass becomes a thick nearly solid yellow paste. Continuous heating at the same temperature causes no further apparent change. This mass, which on cooling is made up of yellow crystals imbedded in a red vitreous matrix, is then dissolved in hot water forming a clear red solution or at most one containing but a small quantity of a brown flocculent precipitate. This solution is filtered if necessary and evaporated to a small volume from which the substance separates on cooling in reddish yellow radial crystals. These are filtered and washed with ether till the washings are perfectly colorless. The substance on repeated crystallization from water has a pale straw yellow color and when deposited slowly forms transparent crystal blocks from 2·6 mm long, arranged in radial groups.

A considerable amount of resorcin is lost by sublimation during the reaction especially if the operation is carried on in a beaker so that some excess should be added. But even when the resorcin is present in excess at the end of the reaction some free acid is always left which may be obtained from the mother liquid in the characteristic colorless orthorhombic crystals.

The water of crystallization and sulphur were determined in the new compound. In estimating the water, the substance was heated to 106°-123° for about ten hours till it attained a constant weight. On standing in the air it quickly regains its original weight. When heated to 130°-140° for some time it turns slightly reddish and loses over 10% of its weight which is not regained by standing in the air.

Estimation No. I. was made by fusion with KOH and KNO₃. Nos. II and III were made by Mr. Mindileff by Morse’s method, oxidizing with KMnO₄ in KOH solution.

·3882 gr. heated to 106°-123° lost ·0302 gr. = 8·5%
Calculation for 2H₂O - C₁₉H₁₂O₆S + 2H₂O = 8·9% water.

Calculation for C₁₉H₁₂O₆S + 2H₂O = 7·92% S.

These analyses show with but little doubt that the substance has the composition indicated above i.e. C₁₉H₁₂O₆S + 2H₂O. 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.

and the action of resorcin on this anhydride thus.

The substance thus formed would naturally receive the name SulphonfluoresceÏn from its analogy with 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 SO₂.

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 a?? and a very narrow prism a? and clinodome ??. The angle = 75° and the extinction angle against the ? 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.

Transcriber's Note:

The following table was crossed out on the original. A note on the previous page beside the table was:

“All these calculations are wrong. J.R.”