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 of the
alkaloids, is a tertiary base, that is, contains no replaceable hydrogen
atoms in its molecule. It shows very close relations to pyridine. When