The main product of the action of nitric acid on 9-benzoyltetrahydrocarbazole is, however, a colourless, crystalline substance which melts at 150" with evolution of oxides of nitrogen. This substance has the formula C,, Hl8O4N2, and therefore is produced from benzoyltetrahydrocarbazole, C19H170N, by the addition of nitric acid and there can be no doubt that this addition takes place-in the form of* OH and* NO,-at the double linking (10 ...