DECOC′TION

Syn. Decoct′um , L. An aqueous solution of the active principles of any substance obtained by boiling; also the proce of preparing such solutions. The effect of decoction in water differs greatly from that of infusion. At the temperature of 212° Fahr., the e ential oils and aromatic principles of vegetables are di ipated or decomposed; while by infusion in hot water, in covered ve els, they remain for the most part uninjured. The solvent powers of boiling water are, however, much greater than those of hot water; and many vegetable principles scarcely acted on by the one are freely soluble in the other. This is the case with many of the alkaloids, on which the medicinal virtues of several vegetables depend. On the other hand, the solutions of many substances, though more readily made by boiling, are speedily weakened or rendered inert by ebullition, in consequence of the active principles being either volatilised along with the steam, or oxidised or decomposed by exposure to the atmosphere. This is particularly the case with substances abounding in extractive or astringent matter. When the medicinal properties of vegetables are volatile, or are injured by a strong heat, infusion should be had recourse to, in preference to boiling; but when a solution of the fixed constituents is alone sought, decoction is preferable. The substances employed for making decoctions should be well bruised, or reduced to a very coarse powder, or, if fresh and soft, they should be sliced small. In the former case, any very fine powder or adhering dust should be removed with a sieve, as its presence tends to make the product thick and disagreeable, and also more troublesome to strain. The ve el in which the ebullition is conducted should be furnished with an accurately fitting cover, the better to exclude the air; and the application of the heat should be so conducted that the fluid may be kept simmering, or only gently boiling, as violent boiling is not only quite unnece ary, but absolutely injurious to the quality of the product. In every case the liquor should be strained whilst hot, but not boiling, and the best method of doing this is to employ a fine hair sieve, or a coarse flannel bag. In general it is found that, as decoctions cool, a sediment is formed, in consequence of the boiling water di olving a larger portion of vegetable matter than it can retain in solution when cold. This deposit for the most part consists of the active principles of the solution, and, unle when otherwise ordered, should be mingled with the clear liquid by agitation, when the decoction enters into extemporaneous compositions, or when the dose is taken. The length of time occupied by the ebullition is another point demanding some attention. Long boiling is in no case nece ary, and should be avoided, especially in decoctions prepared from aromatic vegetables, or those abounding in extractive. The Colleges, in such cases, direct the ingredients “to be boiled for a short time,” or “for ten minutes;” or they limit the period of the ebullition by stating the quantity that must be volatilised, as—“boil to a pint, and strain.” The last method is generally employed for those substances that do not suffer by lengthened boiling. In preparing compound decoctions those ingredients should be boiled first which least readily give up their active principles to the menstruum, and those which most readily part with them should be added afterwards. In many cases it is proper simply to infuse the more aromatic substances in the hot decoction of the other ingredients, by which means their volatile principles will be better preserved. Distilled water, or perfectly clean rain water, should alone be used for decoctions, extracts, and infusions. Spring and river water, from containing lime, have much le solvent matter. The aqueous solutions of organic matter, from the nature of their constituents, rapidly ferment or putrefy, at the ordinary temperature of the atmosphere. Neither decoctions nor infusions are fit to be used in dispensing, unle made the same day. They should, consequently, be only prepared in small quantities at a time, and any unconsumed portion should be rejected, as it would be imprudent for the dispenser to risk his own reputation, and the welfare of the patient, by employing an article of dubious quality. It has of late years become a general practice for the wholesale houses to vend preparations under the name of ‘Concentrated Decoctions,’ which, with the exception of the compound decoction of aloes, are stated to be of 8 times the pharma copœial strength; so that one drachm of these liquids added to seven drachms of water forms extemporaneous decoctions, profe edly resembling those of the pharma copœia. The decoction of aloes is made of only four times the usual strength, as the nature of its composition would not permit of further concentration. Such preparations are, however, very imperfect substitutes for the freshly made decoctions. The extreme difficulty of forming concentrated solutions of vegetable matter with bulky ingredients too often leads to the omi ion of a portion of the materials, or to the practice of concentrating the liquid by long evaporation. In the first case the strength is, of course, le than it should be; and in the second, the quality is injured, and perhaps the preparation is rendered nearly inert by the lengthened exposure to heat, and the consequent volatilisation or decomposition of its active constituents. The common practice of adding a considerable portion of spirit to these preparations, which is absolutely nece ary to preserve them, is also objectionable, as, in many of the cases in which decoctions are prescribed, this article, even in small quantities, exerts a prejudicial action. Some concentrated decoctions have been recently offered for sale which do not contain alcohol, being preserved by the addition of sulphurous acid, or sulphite of lime.