CHAPTER XXVII.

ALCOHOLIC LIQUIDS MADE BY PERCOLATION OR

MACERATION.

Tincturæ.

Tinctures.

TINCTURES are alcoholic solutions of medicinal substances. They differ from spirits in being made from non-volatile bodies, there being but one official exception to this rule. They are made by percolation, maceration, solution, or dilution, and the menstrua employed in the official tinctures are alcohol, diluted alcohol of various strengths, aromatic spirit of ammonia, or mixtures of alcohol, water, and glycerin. The official tinctures are seventy-two in number. In some unofficial tinctures, ether, spirit of ether, ammoniated alcohol, and spirit of nitrous ether are used. The use of alcohol as a solvent for the active or useful principles in drugs has been practised for many years, but it has required a long time and much experience to determine the proper proportion of water to dilute the alcohol so that the menstrua should thoroughly exhaust the drugs without extracting the inert principles, and yet contain sufficient alcohol to secure permanent preparations that will not deposit in time a portion of their active constituents. The advantages of alcohol as a menstruum have been proved so thoroughly, that the use of aqueous preparations has greatly declined in this country; and yet there are some instances, particularly in the case of the weak tinctures and those requiring a large dose, in which the therapeutic action of the menstruum almost equals that of the drug. In these cases, however, the physician may prefer the fluid extract when he does not desire the stimulating action of the alcohol in the tincture.

In selecting the menstrua the proportion of water in each case was made as great as possible without endangering the permanency of the preparation, one especial advantage being that such tinctures may be added in small proportions to aqueous preparations without serious precipitation. In this respect tinctures have usually a great advantage over fluid extracts, and weaker alcoholic menstrua are often used successfully for tinctures when such would be entirely unsuitable for fluid extracts, because the tincture, on account of its comparative weakness, having a much larger proportion of menstruum to exhaust the drug with, than the fluid extract, may have the excess over the proportion of alcohol used in the fluid extract made up with water. It has been proved that a pint of diluted alcohol will extract by percolation a larger proportion of the soluble principles of a drug than half a pint of alcohol and half a pint of water percolated separately through the drug.

1 Tincture of Iodine.

The properties of alcohol are considered under another head (Part IV.), yet it seems desirable to notice here the solvent properties of this valuable preservative. It mixes freely with water, ether, acetic acid, a number of volatile oils, and castor oil; it dissolves resins, camphor, tannin, benzoic acid, chlorophyl, the alkaloids, balsams, iodine, ferric chloride, ammonium carbonate, etc. Diluted alcohol extracts from drugs, gum, extractive, chlorophyl, albumen, coloring matter, resins, volatile oils, alkaloids, sugar, tannin, etc. Glycerin is used in tinctures to prevent precipitation by retaining in solution principles which would otherwise in time be deposited.

Preparation.-Tinctures are officially made in three ways: 1. By percolation. 2. By maceration. 3. By solution or dilution.

1. By Percolation.-This is the best method for making tinctures, and it is always directed by the Pharmacopoeia when practicable. Tinctures are made in this way from all drugs which are capable of being readily comminuted and displaced. The special advantages of percolation over maceration and expression are seen in the saving of time and labor, and in the greater efficiency of the product if the process has been carefully and skilfully performed. The introduction of metric measures into the U.S. Pharmacopoeia of 1890 has greatly simplified the working formulas, there being now no calculations necessary to determine the end-product; the employment of metric receiving-bottles in percolating operations secures accuracy within reasonable limits, and their convenience will always be a recommendation. The use of parts by weight for tinctures proved unsatisfactory. If the drugs from which the tinctures are directed to be made could be standardized so that they would always contain a definite and uniform weight of the active principles, there might be an advantage in bringing the endproduct to a weight which would bear a simple relation to the proportion of active principles selected as a standard; but the Pharmacopoeia, for obvious reasons, has not fixed a limit for even the amount of moisture in air-dried drugs, and to assay all of them and fix a maximum and minimum limit of each active principle present in each drug would be impracticable, and in most cases impossible. Now, the variation in the amount of moisture and in the proportion of active principles in commercial drugs is far greater than is generally supposed; and so long as this ever-present bar to uniformity is not overcome, it is useless to regard the trifling advantage supposed to exist in favor of accuracy and convenience in weighing liquids: practically, the question of accuracy resolves itself into one of personal error, for a careful operator will make more accurate tinctures by using measures than a careless one will by using weights, and vice versa. Fifty-seven official tinctures, or more than two-thirds of the whole number, are made by percolation.

2. By Maceration.-This method of making tinctures is officially used in the case of resins, balsams, gums, soap, etc., where the practical difficulties likely to be encountered in percolation would offset any advantages that the latter process might possess (see page 253).

3. By Solution or Dilution.-A few tinctures are made in this way, such as tincture of iodine by dissolving iodine in alcohol, tincture of ferric chloride by diluting the solution of ferric chloride with alcohol.

The following tables exhibit the official tinctures, classified so as to show their relative strength both as to weight and volume, the variations in menstrua, and other useful data:

Table of Official Tinctures arranged in the Order of their Relative Strength, with Other Data.

Mix Alcohol and Water in the proportion of 700 C.c. [old form 22 fl. oz.] of Alcohol to 300 C.c. [old form 91 fl. oz.] of Water. Having moistened the powder with 200 C.c. [old form 6 fl. oz.] of menstruum, macerate for twenty-four hours; then pack it firmly in a cylindrical percolator, and gradually pour menstruum upon it, until 1000 C.c. [old form 2 pints] of Tincture are obtained.

TINCTURA ALOES. U. S. Tincture of Aloes.