Bitter Extractive of Aloes.
Preparation. — Exhaust powdered Aloes with cold water; evaporate the infusion one-half ; add an excess of acetate of lead, which precipitates the gallate, ulmate and albuminate of that metal ; pour into the clear liquor solution of ammonia, which gives a yellowish-orange colored precipitate, consisting of oxide of lead combined with Aloesin, and which must be separated and washed with boiling water, and then decomposed by a current of sulphureted hydrogen, but out of contact with atmospheric air. Sulphuret of lead is deposited, and a colorless liquid floats above it, which must be decanted, and evaporated in vacuo.
History. — Thus prepared, Aloesin is in colorless, or pale-yellow scales, like a varnish, without any sign of crystallization, of a powerful aloetic taste, soluble in cold water, alcohol, and especially weak spirit, sparingly soluble in ether, and not at all in fixed or volatile oils. Its aqueous solution, when exposed to the air, owing to oxidation, becomes dark-red; it is not precipitated by iron salts, acetate of lead, isinglass solution, or infusion of galls. Heat, exposure, and moisture convert it into an insoluble, inert oxygenated extract.
Properties and Uses. — Same as aloes. Eight grains of aloesin being equal to ten of Socotrine, and fifty of Cape aloes.