it takes up a molecule of water and is split into tropine,
C_{8}H_{15}NO, and tropic acid, C_{9}H_{10}O_{3}. This latter is
phenyl-oxypropionic acid. Tropine, when heated to 180 deg.C. with
concentrated hydrochloric acid, splits off a molecule of water, and
yields tropidine, C_{8}H_{13}N, a liquid base, with an odor resembling
conine. When this tropidine is heated with an excess of bromine, it
yields dibrompyridine.

_Piperine_, the alkaloid of pepper, has also been well studied. When
boiled with alcoholic potash solution, it takes up a molecule of water
and splits apart into piperic acid, C_{12}H_{10}O_{4}, and piperidine,
C_{5}H_{11}N. This latter base has been shown to be a hydrogen addition
product of pyridine, C_{5}H_{5}N. When heated with concentrated
sulphuric acid, it is oxidized to pyridine. Piperidine hydrochlorate,
also, when heated with excess of bromine to 180 deg. C., yields
dibrompyridine.

_Sinapine_, the alkaloid which exists as sulphocyanate in white mustard
seed, yields, under the same reaction as that applied to atropine and
piperine, quite different results. When boiled with baryta water,
sinapine decomposes into sinapic acid, C_{11}H_{12}O_{5}, and choline,
C_{5}H_{15}NO_{2}, the latter a well-known constituent of the bile, and
produced also in the decomposition of the lecithin of the brain and yolk
of egg.

_Cocaine_, the alkaloid of coca leaves, is decomposed by heating with
hydrochloric acid into methyl alcohol, benzoic acid, and a crystalline
base, ecgonine, C_{9}H_{15}NO_{3}.

_Caffeine_ and _theobromine_ have also quite different relations.
Caffeine, it will be remembered, is the methyl ester of theobromine, and
can be prepared from it. When caffeine is carefully oxidized with
chlorine, it yields dimethyl-alloxan and methyl-urea. Both theobromine
and caffeine are decomposed by heating to 240 deg. C. in sealed tubes with
hydrochloric acid, identical products being obtained. These products are
carbon dioxide, formic acid, ammonia, methyl-amine, and sarcosine, the
last three being of course in combination with the excess of
hydrochloric acid. The artificial preparation of theobromine and
caffeine from xanthine, and guanine also show clearly their relations.

If, having completed our survey of what has been done in the way of
decomposing the alkaloids by the different classes of reagents, we
review the field, it will be seen that with all the alkaloids mentioned,
except the last four, a mor