Abstract The existence of Narcotine was indicated by Derosne as early as the year 1803, but its chemical nature remained almost entirely unknown until Robiquet, in 1817, showed that it belonged to the class of vegetable alkaloids. Numerous analyses of narco­tine were subsequently published by Dumas and Pelletier, Pelletier, Liebig, Regnault, and others; but its composition was first determined to the general satisfac­tion of chemists by Blyth, who, in 1844, proposed the formula C46 H25 NO14, support­ing it by numerous analyses of the double hydrochlorate of narcotine and platinum, and showing, at the same time, that it accorded well with the most trustworthy results of previous investigators, and also accounted satisfactorily for the formation of the remark-­able decomposition-products of narcotine discovered by himself and by Wöhler. Since the publication of Blyth’s investigation, the formula which he proposed has been generally adopted as expressing correctly the composition of this base. More recently, however, Wertheim, founding his opinion chiefly on the composition of the volatile bases obtained by distilling narcotine with potash, has maintained the existence of two additional varieties of narcotine, homologous with that examined by Blyth, and repre­sented respectively by the formulae C44 H23 NO14 and C48 H27 NO14; while Hinter-berger has analysed a compound of chloride of mercury with what he considers as a fourth variety, still homologous with the preceding, and represented by the formula C42 H21 NO14. Such being the results of previous investigations, it was plainly necessary to begin any new research into the chemical nature of narcotine by endeavouring to ascertain, by direct analysis, whether there existed in reality more than one kind of narcotine, and, if so, which of these kinds was being operated upon. The following are the results obtained on analysing specimens of narcotine procured from several distinct sources.