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 KNO_{3}. Nos. II and III were made by Mr. Mindileff by Morse’s method, oxidizing with KMnO_{4} in KOH solution. ·3882 gr. heated to 106°-123° lost ·0302 gr. = 8·5% Calculation for 2H_{2}O - C_{19}H_{12}O_{6}S+2H_{2}O = 8·9% water. I. ·2007 gr sub. gave ·1286 gr BaSO_{4} = 8·77% S. II. gr ” ” ” gr ” = 7·91” ” III. gr ” ” ” gr ” = 7·89” ” Calculation for C_{19}H_{12}O_{6}S+2H_{2}O = 7·92% S.