the following
formulae:

CH N NH
/ \ / \ / \
HC CH HC CH H_{2}C CH_{2}
| | | | | |
HC CH HC CH H_{2}C CH_{2}
\ / \ / \ /
CH CH CH_{2}

(Benzene,) (Pyridine,) (Piperidine,)
(C_{6}H_{6}) (C_{5}H_{5}N) (C_{5}H_{11}N)

If we introduce six hydrogen atoms into pyridine, we convert it into
piperidine. Ladenburg succeeded in so hydrogenizing pyridine by acting
upon an alcoholic solution with sodium, and from the base which was
formed he obtained a platinochloride which agreed with the similar
double salt of piperidine. He has also prepared it from trimethyline
cyanide by the action of sodium. Pentamethylinediamine is the
principal intermediary product, and this gives piperidine when
distilled with superheated steam. He has proved that the alkaloid so
obtained is identical with that prepared from piperine. Another
curious point which Ladenburg has lately proved is that cadaverine
(one of the products of flesh decomposition) is identical with
pentamethylinediamine, and that its imine is the same as piperidine.
The synthesis of coniine by Ladenburg is one of the most notable
achievements of modern chemistry. He at first supposed that this
alkaloid was piperidine in which two hydrogen atoms were replaced by
the isopropyl radical (C_{3}H_{7}), its formula being taken as
C_{5}H_{9}(C_{3}H_{7})NH. But he has since changed his view, as will
be seen from what follows. In its synthesis 1,000 grammes of picoline
were first converted into alphapicoline, 380 grammes being obtained.
This was heated with paraldehyde, whereby it was converted into
allylpyridine (48 grammes), and this by reduction with sodium yielded
alpha-propylpyridine, a body in almost every respect identical with
coniine. The more important difference was its optical inactivity, but
he succeeded in splitting up a solution of the acid tartrate of the
base by means of _Penicillium glaucum_. Crystals separated which had a
dextro-rotatory power of [_a_]_{D} = 31 deg. 87' as compared with the
[_a_]_{D} = 13 deg. 79' of natural coniine. This brief account conveys but
a faint idea of the difficulties which were encountered in these
researches. Optical methods of examination have proved of great value,
and are destined to play an important part in such work.

A