The Purgative Principle of Barbadoes Aloes.
Preparation. — Pulverize the aloes with sand, and then treat it with cold water ; strain off the liquid, and evaporate it in vacuo to a syrupy consistence — set it aside for a few days, when it will be filled with a mass of brownish-yellow granular crystals. This is impure Aloïne. To remove the brown matter associated with it, re-crystallize it repeatedly from warm water, until the crystals are of a sulphur-yellow. In making these solutions, the temperature of the water should not exceed 150° F. At 212° Aloïne oxidizes rapidly, and is decomposed.
History. — When pure, it crystallizes in stellated groups of small prismatic needles, whose purity is shown by the color, which should not deepen by exposure to the air in desiccation. It is completely neutral, sparingly soluble in cold water, but readily in warm, with a taste, at first sweetish, but soon becoming intensely bitter. Its solutions in the alkalies and their carbonates is of an orange-yellow, and the liquid absorbs oxygen upon contact with the atmosphere, which rapidly deepens its color. Boiled with alkalies or acids, it is speedily transformed into a brown resin. Corrosive sublimate, nitrate of silver, or neutral acetate of lead, do not cause its precipitation ; concentrated subacetate of lead produces a precipitate of an intense yellow, soluble in excess of water, and becoming deeper colored on exposure. Cold fuming nitric acid dissolves it, without disengaging gas ; forming a reddish-brown liquid ; to which, if sulphuric acid be added in great excess, a yellow pulverulent body is thrown down, which explodes when heated. By dry distillation, aloïne furnishes a slightly aromatic, volatile oil, and a quantity of resinous substance. It forms crystallized compounds with bromine, but not with chlorine, although it combines equally well with this latter. Bromine, added to a cold aqueous solution of aloïne, instantly forms a yellow precipitate, while the supernatant liquid assumes a very acid reaction, consequent upon the formation of hydrobromic acid. By dissolving the precipitate in warm alcohol, and cooling the solution, bromated aloïne is obtained in brilliant yellow needles, grouped in stars.
Properties and Uses. — Same as aloes. Dose of aloïne, one-fourth of a grain to a grain.