SULPHAPYRIDINE (M and B 693) is readily hydrolysed by dilute mineral acids1. Many isomerides of sulphapyridine have been made and it has been found that the three isomeric derivatives from 3-aminopyridine (3-(o-, m- and p-aminobenzenesulphonamido)pyri-dine) are stable to hot mineral acids. All but one of the derivatives of 2- and 4-aminopyridine which were tested were found to be more or less easily broken down to the corresponding aminopyridine and an aminobenzene sulphonic acid as is shown below: Conditions, sulphonamide refluxed for 30 min. with 15 percent aqueous hydrochloric acid. 2-(o-aminobenzenesulphonamido)pyridine 35 percent unchanged 2-(p-aminobenzenesulphonamido)pyridine Complete hydrolysis. 4-(p-aminobenzenesulphonamido)pyridine Complete hydrolysis.