{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.

We may now look at the question of the decomposing effect of reagents
upon the alkaloids. The means which have proved most efficacious in
decomposing these bases are the action of oxidizing and reducing agents,
of bromine, of organic iodides, of concentrated acids and alkalies, and
of heat.

Taking up the volatile alkaloids, we find with regard to _conine_,
first, that the action of methyl iodide shows it to be a secondary
amine, that is, it restrains only one replaceable hydrogen atom of the
original ammonia molecule. Its formula is therefore C_{8}H_{16}NH. From
conine can be prepared methyl-conine, which also occurs in nature, and
dimethyl-conine. From this latter has been gotten a hydrocarbon,
C_{8}H_{14}, conylene, homologous with acetylene, C_{2}H_{2}. Conine, on
oxidation, yields chiefly butyric acid, but among the products of
oxidation has been found the pyridine carboxylic acid before referred
to. The formula of conine, C_{8}H_{17}N, shows it to be homologous with
piperidine, C_{5}H_{11}N, a derivative of piperine, the alkaloid of
pepper, to be spoken of later; and, just as piperidine is derived from
pyridine by the action of reducing agents, so conine is probably derived
from a propyl-pyridine. The artificial alkaloid paraconine, isomeric
with the natural conine, will be referred to later.

_Nicotine_, C_{10}H_{14}N_{2}, the next simplest in formula