Chemical Composition—In 1833 Mein prepared from the root, and Geiger and Hesse from the herb, the crystallizable alkaloid Atropine. The researches of Lefort (1872) have proved that the roots contain it in very variable proportions, the young being much richer in alkaloid than the old.[1677] The maximum proportion obtained was 0·6 per cent.; this was from root of the thickness of the finger. Large old roots, 7 or 8 years of age, afford from 0·25 to 0·31 per cent. They have besides a smaller proportion of bark than young roots, and it is chiefly in the bark that the alkaloid appears to reside. Manufacturers of atropine employ exclusively the root.
Ludwig and Pfeiffer (1861), by decomposing atropine with potassium chromate and sulphuric acid, obtained benzoic acid and propylamine. Other products are formed when atropine is treated with strong hydrochloric acid, baryta water or caustic soda, thus—Atropine, C₁₇H₂₃NO₂ + H₂O = Tropic Acid, C₉H₁₀O₃ + Tropine, C₈H₁₅NO.
| Tropic acid, C₆H₅C(OH) |  | CH₃ |
| COOH, |
being further boiled with the same agents is converted into atropic acid,
| C₆H₅C | | CH₂ |
| COOH, |
which, especially by using hydrochloric acid, is gradually transformed into isotropic acid. Both these acids are isomeric to cinnamic acid, C₉H₈O₂, but otherwise remarkably dissimilar.
Tropine is a strongly alkaline body, readily soluble both in water and alcohol, and furnishing tabular crystals by the evaporation of its solution in ether. Neither tropine nor tropic acid, it is stated by Kraut (1863), is present in the leaves and root of belladonna.
Hübschmann (1858) detected in belladonna root a second but uncrystallizable alkaloid, called Belladonnine; it has a resinous aspect, is distinctly alkaline, and when heated emits, like atropine, a peculiar odour.
The root further contains, according to Richter (1837) and Hübschmann, a fluorescent substance, as well as a red colouring matter called Atrosin.[1678] The latter occurs in greatest abundance in the fruit, and would probably repay further investigation.
Uses—Belladonna root is chiefly used for the preparation of atropine, which is employed for dilating the pupil of the eye. A liniment made with belladonna root is used for the relief of neuralgic pains.