35. To Prepare Tinctures

35. To Prepare Tinctures. Tinctures are solutions of vegetable and animal drugs, and sometimes of mineral substances, in spirituous liquids. The spirit most commonly employed is proof-spirit; sometimes rectified spiritis used, and occasionally ether. Ammonia is sometimes conjoined with the spirit, in which case the solution is termed an ammoniated tincture. Rectified spirit is alcohol, with 16 per cent. of water, and its specific gravity is .838. Proof-spirit is composed of 5 parts of rectified spirit mixed with 3 parts of water, the resulting compound containing 47.5 per cent, of water, specific gravity .920. The choice between proof and rectified spirit depends on their respective solvent powers over the active principles of the drugs employed.

Tinctures are usually prepared by reducing the solid ingredients to small fragments, coarse powder, or fine powder, macerating them for 7 days or upwards in proof or rectified spirit, straining the solution through linen or muslin, or paper, and finally expressing the residuum strongly, to obtain what fluid is still retained in the mass. They are also prepared by the method of displacement. (See No. 41 (To obtain Tinctures by Displacement or Percolation).) All tinctures should be prepared in close glass or stoneware vessels, and be shaken frequently during the process of maceration. Tinctures arc better clarified by repose than by filtration, as in the latter case a considerable portion is retained by the filtering medium, and lost by evaporation. In ordinary cases, it will be sufficient to allow the tincture to settle for a few days, and then to pour off the clear supernatant portion through a funnel loosely choked with a piece of sponge or tow, to keep back any floating fragments of straw or other light substances; after which the remaining foul portion of the liquid may be filtered through paper. When it is absolutely necessary to filter a tincture, and the quantity is large, conical bags should be employed. The filtration should be conducted as rapidly as possible, for the double purpose of lessening the amount lost by evaporation, and the action of the air on the fluid. Tinctures long exposed to the air frequently lose their transparency within a few days after their filtration, owing to the oxidation and precipitation of some portion of the matter previously held in solution. Resinous and oily tinctures, as those of myrrh, tolu, and lavender, may be usually restored to their former brightness by the addition of a quantity of spirit, equal to that which they have lost by evaporation; but many tinctures resist this mode of treatment, and require refiltering. Ethereal tinctures are best prepared by percolation, and should be both made and kept in stoppered bottles.

When both the substances are fluid, as in the case of certain balsams, the spirituous solution is made by merely mixing the two together in suitable proportions. For instance - Tincture or essence of Tolu consists of 3 drachms balsam of Tolu and 1 quart of alcohol.

The tinctures of the drug-stores are usually very uncertain and inferior preparations. Not only is their manufacture carelessly conducted, without reference to the respective characters of their ingredients, but the ingredients themselves are often deficient in strength and quantity.

We will now proceed to explain the various methods by which good tinctures are obtained.