The alkaloid atropine has been quite thoroughly studied with results of great interest.  When heated with baryta-water or hydrochloric acid, 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 more or less immediate connection with the pyridine and quinoline bases has been indicated.  The conviction accordingly forces itself upon us that, if we want to attack the problem of building up any of these important alkaloids artificially, we must turn to these bases as our starting point.