this constitution.  But with this granted, the simplest alkaloid formulas, those of conine, C_{8}H_{17}N, and nicotine, C_{10}H_{14}N_{2}, still showed that the amine molecule contained quite complex groups of carbon and hydrogen atoms, and the great majority of the alkaloids—­the non-volatile ones—­contained groups in which the three elements, carbon, hydrogen, and oxygen, all entered.  Hence the difficulty in acquiring a knowledge of the molecular structure of those alkaloids at all comparable with that attained in the case of other organic compounds.  Of course synthesis could not be applied until analysis had revealed something of the molecular grouping of these compounds, so the action of different classes of reagents was tried upon the alkaloids.  Before summarizing the results of this study of the decomposition and alteration products of the alkaloids, a brief reference to a related class of organic compounds will be of assistance to those unfamiliar with recent researches in this field.

It is well known that in coal-tar is found a series of ammonia-like bases, aniline or amido-benzol, toluidine or amido-toluol, and xylidine or amido-xylol, which are utilized practically in the manufacture of the so-called aniline dye-colors.  It is perhaps not so well known that there are other series of bases found there too.  The first of these is the pyridine series, including pyridine, C_{5}H_{5}N, picoline (methyl-pyridine), C_{5}H_{4}N(CH_{3}), lutidine (dimethyl-pyridine), C_{5}H_{5}N(CH_{3})_{2}, and collidine (trimethyl-pyridine), C_{5}H_{2}N(CH_{3})_{3}.  This series is also found in relatively larger proportion in what is known as Dippel’s oil, the product of the dry distillation of bones.

The second series is the quinoline series, including quinoline, C_{9}H_{7}N, lepidine (methyl-quinoline), C_{10}H_{9}N, and cryptidine (dimethyl-quinoline), C_{11}H_{11}N.  The two compounds which give name to these series, pyridine, C_{5}H_{5}N, and quinoline, C_{9}H_{7}N, respectively, bear to each other a relation analogous to that existing between benzol, C_{6}H_{6}, and naphthalene, C_{10}H_{8}; and the theory generally accepted by those chemists who have been occupying themselves with these bases and their derivatives is that pyridine is simply benzol, in which an atom of nitrogen replaces the triad group, CH, and quinoline, the naphthalene molecule with a similar change.  Indeed, Ladenberg has recently succeeded in obtaining benzol as an alteration product from pyridine, in certain reactions.  Moreover, from methyl-pyridine, C_{5}H_{4}N(CH_{3}), would be derived an acid know as pyridine-carboxylic acid, C_{5}H_{4}N(COOH), just as benzoic acid, C_{6}H_{5}COOH, is derived from methyl-benzol, C_{6}H_{5}CH_{3}, and from dimethyl-pyridine, C_{5}H_{3}N(CH_{3})_{2}, an acid known as pyridine-dicarboxylic acid, C_{5}H_{3}N(COOH)_{2}, just as phthalic acid, C_{6}H_{4}(COOH)_{2}, is derived from dimethyl-benzol, C_{6}H_{4}(CH_{3})_{2}.  The same thing applies to quinoline as compared to naphthalene.