The following are some of the general methods of preparing alkaloids: -
(1) Base insoluble in water, non-volatile, and existing in the plant in an insoluble form. The bruised plant is boiled or macerated in water acidulated with hydrochloric or acetic acid, and the liquor, after filtration, is neutralized with an alkali (arpmonia, potash, lime, or magnesia); the resulting precipitate is purified by re-solution in dilute acid, digestion with a little animal charcoal, •and subsequent crystallization, or re-precipitation with an alkali; or the first precipitate is purified by dissolving once, or, if necessary, several times in boiling alcohol, which yields the pure alkaloid either on cooling or by evaporation.
(2) Base insoluble in water and nonvolatile, but existing in the plant as a soluble salt. The bruised or sliced plant is boiled or macerated in water, and the filtered liquor is precipitated and otherwise treated as in (1).
(3) Base soluble in water and nonvolatile. An infusion made with very dilute acid, hydrochloric or acetic, is concentrated by gentle heat, and the residual liquor is treated with potash (or concentrated solution of ammonia) and ether conjointly; after repose, the ethereal solution is decanted and evaporated. For those alkaloids which are insoluble in ether (as morphine and cinchonine), the previous process may be adopted.
(4) Base both soluble in water and volatile. The vegetable, in a bruised or divided state, or its extract, is alkalized with potash and distilled; the distillate is neutralized with dilute oxalic or sulphuric acid and carefully evaporated to dryness; the residue is next digested in alcohol, and the resulting tincture agitated with potash and ether, the former being in quantity just sufficient to seize on all the acid; lastly, the ethereal solution thus formed, on careful evaporation, leaves the alkaloid nearly pure. It may be further purified by cautious distillation.
As some of the alkaloids are soluble in excess of the alkaline precipitant, over-saturation should be carefully avoided, or the precipitant may be used under the form of carbonate or bicarbonate. When lime and magnesia are employed, they are boiled for a few minutes with the solution.