The methods employed by earlier investigators when they wished to isolate their diazo compounds was to suspend the substance to be diazotized in alcohol, and then pass in nitrous fumes generated by dropping concentrated nitric acid onto arsenious oxide. The diazo compound from ortho toluidine sulphonic acid is so nearly insoluble in water that it was found possible to diazotize it in water suspension, and generate the nitrous fumes in the solution itself by adding a solution of sodium nitrite to the water suspension containing hydrochloric acid. After a short time the diazo compound separates out and can be filtered off, washed and dried. It is a very stable substance as compared with other diazo compounds. This method was worked out, there being no mention of it in the literature. SULPHONATION OF ORTHO TOLUIDINE Of the possible sulphonic acids of ortho toluidine the commercial product of former days was the one in which the sulphonic acid group was in the para position to the amino group, and meta to the methyl group; thus this acid could find use in preparing the toluene meta sulphonic acid if a method of replacing the amino group by hydrogen could be found. This acid is not now on the market in America because of its limited use in dyestuffs. It is mentioned in Schultz and Julius, (“Farbestoff Tabellen”, 1894 Edition, Trans. by F. C. Green), Cain, (“The Manufacture of Intermediate Products for Dyes”) and Nevile and Winther, (Ber. d. chem. Ges. 13, 1940.), which latter give a method of preparation which was used industrially,--the baking of ortho toluidine sulphate. Their description is rather indefinite but after a few preliminary trials a suitable method was found. I will describe all the experiments attempted, and include the one finally adopted. The ortho toluidine used was (“Practical.”) obtained from Eastman Kodak Co. Experiment 1. Ortho toluidine was suspended in water and conc. sulphuric acid added with vigorous stirring until all the amine had dissolved. The solution was heated to boiling until the sulphate had dissolved, and then cooled and the crystals thus obtained filtered off and dried. This was then powdered and ground with some powdered oxalic acid. These mixtures with and without oxalic acid were then baked until a sample was completely soluble in sodium hydroxide. The mass had become a deep grayish purple. It dissolved in water to give a deep red solution. Nothing satisfactory was obtained from any of these bakes, the formation of a red dyestuff as mentioned by Nevile and Winther seeming to be formed in a great quantity and very easily. Hence this method was discarded. Experiment 2. In this case an excess of sulphuric acid was used. After the oxalic acid had all been decomposed or driven off the mass turned black and became very pitchy. Nothing could be done with it so it was thrown away. Experiment 3.