bulk of the menstruum. The solvent is forced through the mass by pressure obtained from a column of liquid 10 or 12 feet in height, supplied by a reservoir.

Management of the Process of Percolation.-The Pharmacopoeia gives the following directions for conducting percolation, which are applicable to all official preparations in which this method of solution is indicated, as in each individual case the fineness of powder, the quantity of menstruum to be used for moistening the drug, and the degree of firmness with which it is to be packed are specified:

"The percolator most suitable for the quantities contemplated by the Pharmacopoeia should be nearly cylindrical or slightly conical, with a funnel-shaped termination at the smaller end. The neck of this funnel end should be rather short, and should gradually and regularly become narrower toward the orifice, so that a perforated cork, bearing a short glass tube, may be tightly wedged into it from within until the end of the cork is flush with its outer edge. The glass tube, which must not protrude above the inner surface of the cork, should extend from 3 to 4 Cm. beyond the outer surface of the cork, and should be provided with a closely fitting rubber tube, at least one-fourth longer than the percolator itself, and ending in another short glass tube, whereby the rubber tube may be so suspended that its orifice shall be above the surface of the menstruum in the percolator, a rubber band holding it in position.

"The percolator is prepared for percolation by gently pressing a small tuft of cotton into the space of the neck above the cork, and this may then be moistened by pouring a few drops of the menstruum upon the cotton, to facilitate the passage of the first portion of the percolate, which is often very dense.

"The powdered substance to be percolated (which must be uniformly of the fineness directed in the formula, and should be perfectly air-dry before it is weighed) is put into a basin, the specified quantity of menstruum is poured on, and it is thoroughly stirred with a spatula or other suitable instrument until it appears uniformly moistened. The moist powder is then passed through a coarse sieve -No. 40 powders and those which are finer requiring a No. 20 sieve, while No. 30 powders require a No. 15 sieve for this purpose. Powders of a less degree of fineness usually do not require this additional treatment after the moistening. The moist powder is now transferred to a sheet of thick paper and the whole quantity poured from it into the percolator. It is then shaken down lightly and allowed to remain in that condition for a period varying from fifteen minutes to several hours, unless otherwise directed; after which the powder is pressed by the aid of a plunger of suitable dimensions, more or less firmly in proportion to the character of the powdered substance and the alcoholic strength of the menstruum; strongly alcoholic menstrua, as a rule, permitting firmer packing of the powder than those weaker. The percolator is now placed in position for percolation, and the rubber tube having been fastened at a suitable height, the surface of the powder is covered by an accurately fitting

disk of filtering-paper or other suitable material, and a sufficient quantity of the menstruum poured on through a funnel reaching nearly to the surface of the paper. If these conditions are accurately

observed, the menstruum will penetrate the powder equally until it passes into the rubber tube, and reaches in this a height corresponding to its level in the percolator, which is now closely covered to

prevent evaporation. The apparatus is then allowed to stand at rest for the time specified in the formula.

"To begin percolation, the rubber tube is lowered and its glass end introduced into the neck of a bottle previously marked for the quantity of liquid to be received, if the percolate is to be measured, or of a tared bottle if the percolate is to be weighed; and by raising or lowering this recipient the rapidity of percolation may be increased or lessened, as may be desired. A layer of menstruum must constantly be maintained above the powder, so as to prevent the access of air to its interstices, until all has been added or the requisite quantity of percolate has been obtained. This is conveniently accomplished, if the space above the powder will admit of it, by inverting a bottle containing the entire quantity of menstruum over the percolator in such a manner that its mouth may dip beneath the surface of the liquid, the bottle being of such a shape that its shoulder will serve as a cover for the percolator. (For illustration of the official process, see Fig. 109.)

"It is obvious that the success of the process of percolation largely depends upon the regulation of the flow of the percolate; if this should be too rapid, incomplete exhaustion will result; but if too slow, valuable time may be wasted. The rate of flow for extracts and fluidextracts for 1000 Gm. of powder should range from 2 to 5 drops a minute; for official quantities of tinctures and preparations of about the same strength from 8 to 15 drops a minute; it is evident that the proper rate of flow should vary with the quantity and character of the drug employed and the density of the menstruum."

The degree of fineness of powder to which a drug is to be reduced depends partly upon the menstruum to be used and partly upon the nature of the active constituents of the drug and the readiness with which these can be extracted. Drugs like aconite, cinchona, nux vomica, veratrum viride, and others, require to be in fine powder; while gentian, rhubarb, krameria, squill, and the like, can be readily exhausted in coarser powder. As a rule, strongly alcoholic or ethereal menstrua are used with fine powders, whereas hydro-alcoholic and aqueous menstrua are better adapted to coarser powders.

The quantity of menstruum to be used for moistening the powder also varies with different drugs; one-fourth to one-half as much menstruum as powder is generally required to dampen it thoroughly without destroying its mobility, depending likewise upon the nature of the drug and menstruum. In a few cases, where the active constituents are quickly extracted, and previous moistening might cause the powder to agglutinate, as in the case of the official oleoresins, it is even better not to moisten the drug at all before placing it in the percolator.

The next step is the proper packing of the percolator, and upon it will largely depend the success of the process. A suitable support must be provided for the moistened powder, and for this purpose a notched cork or a tuft of absorbent cotton may be used. If cork

be chosen, a layer of cotton should be placed over it to prevent the escape of powder; or if cotton alone be used, it may be slightly compressed into the neck of the percolator. Unless the quantity of drug be large, the moistened powder, after having been first passed through a coarse sieve to break up any lumps, should be transferred to the percolator all at one time, and then shaken down by tapping the sides of the vessel. If the drug is to be saturated with menstruum before maceration, as in the case of fluid extracts, the powder should be at once compressed, moderately or firmly, as the character of the menstruum and the nature of the drug may require. As a rule, fine powders and alcoholic menstrua demand firm packing, as also ligneous and spongy drugs under certain conditions; aqueous menstrua generally necessitate moderate compression. If the moistened drug be introduced in layers, uniform packing becomes more difficult; the lower portions of the drug should be less firmly compressed than the upper layers, because the menstruum, when it reaches them, being already charged with some soluble matter, is denser than at the top, and hence cannot penetrate a firmly packed mass as readily as would fresh menstruum. Maceration of the moistened powder prior to percolation is advantageous in many cases, as it allows the drug to swell and become more thoroughly permeated by the menstruum, and permits more satisfactory packing afterward; in some cases, where concentrated solutions are desired, maceration after saturation is positively necessary to insure good results. The packing of the moistened powder is best effected with a packing stick of suitable design, made of hard wood, of the shape of the well-known potato-masher. Next to uniformity in fineness of powder, uniformity in packing is the most important feature in percolation, so as to insure the even descent of the menstruum; if the drug is more firmly compressed on one side than on the other, the menstruum is sure to flow in the direction of least resistance, and leave a part of the mass imperfectly extracted. After the powder has been packed, a diaphragm of filtering paper or felt is laid over the surface and kept in place by means of pebbles or pieces of broken glass; this is for the purpose of preventing disturbance of the upper layer and to insure equal distribution of the liquid when the menstruum is poured on.

1

FIG. 110.

GAL

12t

1Pt

-128

-112

Glass receiving jar, graduated in U.S. fluid measure.

As stated in the pharmacopoeial directions, a layer of menstruum must constantly be maintained above the powder, in order to prevent access of air to its interstices. Every percolator should be provided with a cover, which may be either of glass or sheet-rubber, to avoid loss of or change in the menstruum.

The simplest arrangement for controlling the rate of flow of the

percolate is by means of a rubber tube, as specified in the official directions, and this device can be attached to nearly every form of percolator known. As the rate of flow from the tube will be proportionate to the difference in height between the liquid in the percolator and the point to which the tube is raised on the outside, it is evident that its control is within easy reach, and may be varied from a constant stream to 2 drops per minute. The rapidity with which the percolate shall be allowed to pass will vary with the object in view and the ease with which the active principles enter into solution; for tinctures, the average rate may be stated to be 8 to 15 drops per minute, while the percolate in the case of fluidextracts should not be allowed to flow faster than from 2 to 5 drops per minute.

The complete exhaustion of a drug can only be judged by the physical properties of the last portions of the percolate; hence a thorough knowledge of the valuable constituents sought to be extracted is essential; absence of color and odor is not always indicative of perfect exhaustion, and the sense of taste furnishes a more reliable test in the case of aconite, ginger, nux vomica, etc. Drugs like jalap and podophyllum are known to be exhausted when the percolate mixes clear with water, as this will not occur until all resin has been extracted. Cardamom, valerian, vanilla and similar

aromatic drugs are judged entirely by the odor of the percolate; quassia, rhamnus and gentian, by the bitter taste; and rhatany, catechu, and geranium, by the peculiar astringency of their soluble constituents.

A considerable quantity of alcoholic menstruum is sometimes