CO / \ COCl / N.NH₄ / / / C₆H₃——SO₂Cl + 4NH₃ = C₆H₃——SO₂ + 2NH₄Cl. \ \ NO₂ NO₂ while the lower melting chloride is quickly transformed into the ammonium salt of paranitroorthocyanbenzenesulphonic acid: CCl₂ / \ / O CN / / / C₆H₃——SO₂ + 4NH₃ = C₆H₃——SO₂ONH₄ + 2NH₄Cl. \ \ NO₂ NO₂ Gray’s study of the symmetrical chloride was confined for the most part to the preparation of a series of salts of this latter acid, and to an investigation of the action of aniline upon the chloride itself. It was thought to be of interest to extend this study to a wider range of reactions, as well as to improve, if possible, the method of preparing the chloride in pure condition. At the suggestion of Prof. Remsen this work was accordingly undertaken. II. Preparation of Material. The method employed in the preparation of paranitroorthosulphobenzoic acid was essentially that described by Hart,[7] Kastle,[8] Gray[9] and Hollis.[10] The details of it are repeated here for the purpose of calling attention to certain facts that came under the author’s notice. [7] Am. Chem. Journ. I, 350. [8] Ibid XI, 177. [9] Inaug. Diss. J. H. Univ. 1845. [10] Inaug. Diss. J. H. Univ. 1896. 100 grams of paranitrotoluene are added to 400 grams of fuming sulfuric acid, and the mixture heated in a balloon flask at 100° on a water bath. The heating is continued until a few drops of the mixture, added to cold water, dissolves completely to a clear solution. The time required for this operation varies much with the conditions. Continued stirring very considerably hastens the reaction, as paranitrotoluene forms a layer on the acid, which presents a small surface to its action. With constant stirring the reaction is complete in a few hours, whereas if no stirring is resorted to, as much as several days may be required, especially when large quantities are employed at one time. When the reaction is complete, the mixture is poured into a large volume of water, and neutralized with calcium carbonate. In the filtrate from calcium sulphate, the calcium salt of paranitroorthotoluene sulphonic acid is found, and this is converted into the potassium salt in the usual way. The oxidation of the potassium salt is effected as follows. 50 grams of the salt are dissolved in 2½ litres of water, and to this is added a solution of 15 grams of potassium hydroxide. The mixture is heated to 100° on a water-bath, and when this temperature is reached, 110 grams of potassium permanganate are added. Heating is continued until the solution is decolorized, care being taken to prevent the evolution of free oxygen.