_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° 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° 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