sive portions of menstruum in such a manner that the liquid, as it traverses the powder in its descent to the recipient, shall be charged with the soluble portion of it, and pass from the percolator free from insoluble matter.

When the process is successfully conducted, the first portion of the liquid, or percolate, passing through the percolator will be nearly saturated with the soluble constituents of the substance treated; and if the quantity of menstruum be sufficient for its exhaustion, the last portion of the percolate will be destitute of color, odor, and taste, other than that possessed by the menstruum itself.

The percolator most suitable for the quantities contemplated by this Pharmacopoeia should be nearly cylindrical, or slightly conical, with a funnel-shaped termination at the smaller end. The neck of this funnelend 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 one and one-eighth to one and one-half inch (3 to 4 centimeters) 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. The shape of a percolator should be adapted to the nature of the drug to be operated upon. For drugs which are apt to swell, particularly when a feebly alcoholic or an aqueous menstruum is employed, a conical percolator is preferable. A cylindrical or only slightly tapering percolator may be used for drugs which are not liable to swell, and when the menstruum is strongly alcoholic, or when ether or some other volatile liquid is used for extraction. The size of the percolator selected should be in proportion to the quantity of drug extracted. When properly packed in the percolator, the drug should not occupy more than two-thirds of its height. The percolator is best constructed of glass or stoneware, and is prepared for percolation by gently pressing a small tuft of cotton into the space of the neck above the cork, a small layer of clean and dry sand being then poured upon the surface of the cotton to hold it in place.

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, whilst 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 the 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 has passed into the rubber tube and has reached, in this, the height corresponding to its level in the percolator, which is now closely covered to prevent evaporation, and the apparatus allowed to stand at rest for the time specified in the formula.

FIG. 313.

FIG. 313a.

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 percolated, 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 desirable, observing, however, that the rate of per

Official percolation.

colation, unless the quantity of material taken in operation is largely in excess of the pharmacopoeial quantities, shall not exceed the limit of ten to thirty drops in a minute. 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 shape that its shoulder will serve as a cover for the percolator.

Fig. 313a illustrates an official percolation (U. S. 1880), the shape of the percolator and the arrangement of the exit-tubes being strictly according to the directions.

Shape of the Percolator.-In the U. S. Pharm. 1880 the shape and size of the cylindrical percolator preferred for pharmacopoeial operations were definitely fixed (see Fig. 313). There can be no question that the glass cylindrical percolators (see Fig. 314) commonly furnished by the

FIG. 314.

manufacturers are proportionally too broad for use in percolating drugs for fluid extracts FIG. 315. where the quantity of drug is large in pro

Plain percolator.

Oldberg's percolator.

Conical percolator.

portion to the quantity

of menstruum; but for ordinary tinctures, where the conditions are reversed, they answer admirably. The inference then is obvious, the pharmacist should have per

colators not only of dif

ferent sizes, but also of

different shapes. Fig.

315 shows the narrow

percolator recommended

by Prof. Oldberg. It is narrower than the cylindrical percolator directed by the U. S. Pharm. 1880. The studies on percolation during the last half-century have been directed towards simplifying the process, and the elaborate apparatus of Count Real and others has been replaced by the ordinary percolator and funnel. The conical percolator of the Pharmacopoeia is understood to be a glass funnel (see Fig. 316).

Judgment is required in selecting a percolator for an operation. In making a fluid extract a comparatively narrow percolator should be chosen, because it is desirable that the menstruum should traverse a higher column of powder, for every drop of the menstruum must be economically applied. The rate of flow of the percolator is thereby proportionally diminished, the percolate becomes saturated more rapidly, and thus the operation is more easily controlled, provided the limit has not been exceeded. The character of the drug influences the limit. For instance, one which contains a large quantity of soluble matter, like kino, could not be successfully percolated in a narrow percolator, because the percolate would soon become so dense that it would cease to descend. In making tinctures and weaker preparations, a wider percolator is to be preferred, because the quantity of menstruum is greatly in excess of the quantity necessary to exhaust the drug, and more rapid action is desirable. Figs. 317, 318, and 319 show three percolators of the same height, but of very different shapes. Exactly the same weight of powder is represented in each. The great difference in the height of the columns of powder will be readily noticed, and illustrates the necessity for judgment in selecting percolators. If a fluid extract from the drug is to be made, the tall percolator, Fig. 317, should be chosen ; if a strong tincture, Fig. 318 indicates the shape; whilst for a weak tincture, the funnel shown in Fig. 319 would be preferred; it being

understood that in each case the drug chosen is not an exceptionally difficult one to percolate.

The Degree of Comminution proper for each Substance must depend upon the physical structure of the drug, the ease with which the menstruum dissolves the active or desirable constituents, the length

of time required to exhaust the powder, and the relative proportion of menstruum to drug. Nux vomica and ignatia are drugs having a tough, horny structure, in which the soluble constituents are embedded. If these drugs are to be quickly exhausted of their soluble principles, they must be in fine powder. On the other hand, gentian and rhubarb are drugs which part easily with their active constituents, because their structure is loose and quickly penetrated by the menstruum: therefore these may be readily exhausted when in coarse powder. The relative proportion of menstruum to drug also has a bearing in determining the fineness of the powder, for it is clear that if a fluid extract is to be made in which one hundred volumes shall represent one hundred parts by weight of the drug, the powder should be a finer one than would be required for a tincture where one hundred volumes are used to exhaust ten parts by weight of the drug. In all cases, whether coarse or fine powder is directed, the powder should be uniformly divided; and where the degree of fineness is specified, but a small proportion of the powder should be capable of passing through a sieve of the next higher grade of fineness, and this small proportion should be thoroughly distributed through the powder. The object of this is to permit the uniform descent of the liquid, for fine particles offer more resistance to the passage of the menstruum than coarse ones; and if the powder is not uniform, and the finer particles are deposited upon one side of the percolator, imperfect exhaustion may occur, through the passage of the greater portion of the menstruum upon the side of least resistance,i.e., through the coarser particles. After the powdered drug is moistened, it should be passed through a riddle or coarse sieve several times,

to render it uniform. The little sifter shown in Fig. 218 has been found very efficient for this purpose.

Moistening of the Powder.-The general rule in percolation is to moisten the powder, and there are very few instances in the official processes where it is not directed. The object of moistening the powder is very apparent. If a perfectly dry sponge is held in the hand and a gentle stream of water poured upon it, it will be noticed that very little water is absorbed by it; but if the sponge is thoroughly soaked, and all the water squeezed out that possibly can be, it will be found that it will greedily absorb water. Most drugs are vegetable substances which in their natural state were moist. The process of desiccation has hardened and dried the tissues, so that, like the sponge, they do not absorb moisture quickly, and when compressed, as they are when packed in a percolator, the resistance is still greater. If a dry powder, like ground orange-peel, is tightly packed in a glass percolator and water poured upon it, it will be noticed that the water will penetrate the powder but a short distance. Its further passage is prevented by the particles which are immediately in contact with the water, which have become swollen to such a degree that they press tightly against the sides of the percolator, and thus entirely overcome the gravitating force and penetrating power of the water. If, on the other hand, the powdered orange-peel is moistened with sufficient water to satisfy its tendency to swell, before it is packed in the percolator, the addition of water is followed by its slow percolation through the mass without stoppage, and the utility of moistening the powder is thus proved.

The special cases in which the powder should not be moistened are those in which the addition of menstruum would produce adhesiveness and cause the powder to form lumps that could not be easily penetrated, those in which the moistened powder would offer too little resistance to the passage of the menstruum, and those in which the menstruum is too volatile or too inflammable to render moistening desirable or safe. An instance of the first case is found in the so-called cold percolation of sugar in making syrups; instances of the second and third cases, in the preparation of the oleoresins where ether is used as the

menstruum.

Packing the Powder.-The official directions with regard to this important part of the process of percolation vary continually. Where the degree of pressure is immaterial, no special directions are given. Where there is a likelihood of too much pressure being exerted, so that percolation would cease before it should, the directions are, "pack it moderately;" on the other hand, if there is danger of the operator allowing the menstruum to pass through too rapidly, so that the drug would not be exhausted of its activity, the directions are, "pack it firmly." The proper degree of pressure can be judged only from the character of the drug and the nature of the menstruum. If a porous, spongy drug is to be percolated with a menstruum largely aqueous, it must be moderately packed; but if the menstruum is alcoholic, it must be firmly packed. Before beginning to pack the powder, the throat of the funnel or of the percolator must be obstructed by a loose plug of absorbent cotton or a deeply-notched cork (see Fig. 320), or by some