This chloride was first separated from its unsymmetrical isomer by Gray[12]. It was obtained by allowing a chloroform solution of the mixed chlorides to evaporate until the chloroform had almost entirely disappeared. In the thick liquid so obtained, crystals of the symmetrical chloride were formed. It was also obtained by applying the method devised by Bucher in connection with the corresponding chloride of orthosulphobenzoic acid—i.e. by the action of dilute ammonia on the mixed chlorides. Gray also found that the best conditions for securing a relatively large proportion of the symmetrical chloride were, the employment of as low a temperature as possible in the formation of the chlorides, and of as small an excess of phosphorus pentachloride as would suffice for the reaction. [12] Inaug. Diss. J. H. Univ. 1895. After many experiments, under widely differing conditions, the following method of procedure, embodying the results of Gray’s work, was adopted. Dehydrated acid potassium salt of paranitroorthosulphobenzoic acid, and phosphorus pentachloride, in the ratio of 40: 55 grams, are brought together in a mortar and intimately mixed. The mixture is put into an evaporating dish, and placed on a sulphuric acid bath, previously heated to 150°. As soon as the action has been well started, the dish is removed, and the reaction allowed to proceed without further heating. When it is complete, and the contents of the dish has cooled down to the temperature of the room, the oily product is poured slowly into a salts bottle containing ice water, the bottle being frequently shaken during the process. The shaking is continued with renewed portions of water, as long as the wash water is cloudy. The water is then poured off, the brownish gummy chloride dissolved in chloroform, and the solution placed in a good-sized separating funnel. Ice water is then added, and the contents of the funnel treated with successive portions of ammonia (desk ammonia diluted one half). Shaking is continued after each addition until the odor of ammonia has disappeared, and ice is added from time to time as may be required. When it is found that the odor of ammonia persists after several minutes’ shaking, the chloroform layer, which is usually filled with a solid substance that has separated during the process, is drawn off, filtered, and dried with calcium chloride. By this process all of the unsymmetrical chloride is converted into the ammonium salt of paranitroorthocyanbenzenesulphonic acid, according to the equation: CCl₂ / \ / O CN / / / C₆H₃——SO₂ + 4NH₃ = C₆H₃——SO₃NH₄ + 2NH₄Cl. \ \ NO₂ NO₂ while the symmetrical chloride remains for the most part unchanged, though some of it is converted into the ammonium salt of paranitrobenzoic sulphinide: