The material mentioned above as being the final product from the sulphonation of para toluidine, obtained in a yield of twenty grams or ten per cent yield and then uninvestigated, has since been identified as the acid I was looking for, or para toluidine meta sulphonic acid. A small amount was cooled and diazotized in the usual manner; the diazo compound seemed to be insoluble in the amount of water used, for a white crystalline needle-like precipitate appeared. This was decomposed by boiling with dilute nitric acid (Nevile and Winther, loc. cit.), and on cooling small tufts of yellow needles separated. These were filtered off and dried, then recrystallized from alcohol. The best portions of these were then recrystallized from ether and the melting point determined. They melted at 79.5-79.8 (uncorr.). Nevile and Winther gave 79-80, showing that they did not purify their compound. The product is dinitro para cresol, or 3-nitro, 4-hydroxy, 5-nitro toluene. DIAZOTIZATION OF ORTHO TOLUIDINE SULPHONIC ACID. Nevile and Winther (loc. cit.), stated that they obtained a diazo compound from their ortho toluidine sulphonic acid and described a few properties, but gave no details of manipulation, so I made several trials to determine the best acceptable method. Experiment 1. I suspended some ortho toluidine sulphonic acid in denatured alcohol, and passed in a rapid current of nitrous fumes, generated by dropping concentrated nitric acid into a saturated solution of sodium nitrite, for fifteen minutes. The suspension became slightly warm, and rather pasty at the end. I allowed it to stand a half hour, and at the end of that time it had become very thick and pasty. I then filtered it off by suction, washed with ether, and dried. Experiment 2. The procedure used was the same as above using ethyl alcohol in place of denatured alcohol, but for some reason no diazotization appeared to take place. The acid was filtered off and used again. Experiment 3. A saturated water solution of the acid was made by boiling some of it up with water, cooling and filtering. No precipitate appeared on passing in nitrous fumes. Experiment 4. Some of the acid was dissolved in sodium carbonate solution, sodium nitrite solution added, and after cooling, concentrated hydrochloric acid added drop by drop. Nitrous fumes were given off, but no precipitate appeared. Experiment 5.