colate 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 (three to four centimetres), 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 dimensions of such a percolator, conveniently holding 500 grammes of powdered material, are preferably the following: Length of body, fourteen inches (36 centimetres); length of neck, two inches (5 centimetres); internal diameter at top, four inches (10 centimetres); internal diameter at beginning of funnel-shaped end, two and one-half inches (6.5 centimetres); internal diameter of the neck, one-half inch (12 millimetres), gradually reduced at the end to two-fifths of an inch (10 millimetres). It is best constructed of glass, but, unless so directed, may be constructed of a different material.

"The percolator is prepared for percolation by gently pressing a small tuft of cotton into the space of the neck above the cork, and a small layer of clean and dry sand is 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 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 position 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.

"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 percolation, 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.

"When the dregs of a tincture, or similar preparation, are to be subjected to percolation, after maceration with all or with the greater portion of the menstruum, the liquid portion should be drained off as completely as possible, the solid portion packed in a percolator, as before described, and the liquid poured on, until all has passed from the surface, when, immediately, a sufficient quantity of the original menstruum should be poured on to displace the absorbed liquid, until the prescribed quantity has been obtained."

The foregoing officinal directions cover the whole general subject of percolation, and the remarks which follow are intended as special consideration of improved methods, and the difficulties which may arise in applying a general rule to the treatment of a variety of substances.

The fineness of powder to be used for percolation has been discussed under the article on fineness of powders, but it may be here repeated that the powders directed in the formulæ of the pharmacopiæ are, as a rule, too fine for successful percolation, and that the mass of druggists will have "better luck" to choose a grade coarser powder than is specified in the officinal formulæ.

Moistening the drug is discussed in the officinal process, and in the article on maceration, and it need only be remarked that it is of great importance to have the drug thoroughly and evenly moistened. Many druggists are in the habit of putting the drug in the percolator and pouring the menstruum upon it to moisten it, without even stirring it up; this should never be done, for, frequently, a portion of the drug will "cake so that it will not become moistened during the entire process of percolation. The drug should always be moistened in a basin or other vessel, before putting into the percolator.

Macerating before percolating is discussed in the article on maceration. It may be here repeated, however, that when water is used as a portion of the menstruum for percolation,

the drug should be moistened with the menstruum and allowed to macerate for twenty-four hours, in order that it may swell before, instead of after, packing in the percolator.

Packing the percolator. In packing the percolator, much depends upon the nature of the drug, the fineness of the powder, etc. Loose, fibrous, or bulky drugs, such as arnica, stillingia, buchu, etc., cannot be packed very firmly, but should be made as compact as possible; heavy drugs, such as aconite root, valerian, golden seal, etc., do not require so much pressure, but will pack much firmer; soft, spongy, or gummy drugs, such as rhubarb, colocynth or squill, should not be packed very firmly; coarse powders, as a rule, should be packed more firmly than fine. The percolator should be packed from the outside towards the centre and as evenly as possible. A disc of paper and then a cover of perforated tin should be placed upon the surface of the powder after it is packed to secure the even distribution of the menstruum as it is poured upon the drug. A glass or earthenware weight may be used with advantage to hold the drug in its place. It should generally be allowed to macerate for some time after the menstruum is poured on before beginning to percolate.

The flow of percolate may be regulated by the rubber tube, as directed in the officinal process; by a loose cork in the bottom of the percolator; or, if the water-bath percolator is used, by the stop-cock. The rapidity with which the percolate should flow, depends very much upon the nature of the drug, and the quantity required to be obtained as compared with the quantity of drug being percolated; for example, fluid extracts should not be percolated so rapidly as tinctures, nor aconite as rapidly as buchu.

With a certain class of drugs, the alcoholic or hydro-alcoholic menstruum, with which the percolation is conducted, may be forced out by adding water after the menstruum has disappeared from the surface of the drug, and thereby make a saving of alcohol, but with others, which soften or make precipitates with an aqueous menstruum, the percolation must be conducted to the end with the same menstruum. The menstruum remaining in the drug after percolation, may be pressed out with a tincture press and the alcohol recovered from it by distillation.

DRUGS DIFFICULT TO PERCOLATE.

Many drugs present difficulties to the ordinary methods of percolation and require special treatment; this is generally

given in the formulæ in which they are found; but they may be classed in a general way as follows:

Ist. Drugs that soften or make a pulpy mass upon the addition of the menstruum, such as orange, gentian, rhubarb, squill, colocynth, etc. Such drugs should be well moistened and macerated before packing; they should be rather coarsely powdered and rather loosely packed, and the percolation, when begun, should be conducted rapidly, and continued to the end with the same menstruum.

2d. Gums and gum-resins which agglutinate or together when the menstruum is added. These should be mixed with an equal bulk of sand, sawdust, or rice chaff, and not packed, but placed loosely, in the percolator, and the percolation conducted in the usual manner.

3d. Bulky drugs, like arnica, buchu, chamomile, etc. Although these drugs are not difficult to percolate, they absorb so much menstruum that the expense of making their preparations is considerably increased. These should be packed as firmly as possible, and held down in the percolator with a weight during the process of percolation.

ECONOMY IN PERCOLATING AND FILTERING.

Much loss of Alcohol occurs by evaporation when the ordinary percolator or filtering funnel are left uncovered during percolation or filtration. To remedy this difficulty a simple apparatus may be constructed by any druggist who will take the trouble. It is shown in use in the following cut :

A, is the wooden cover, large enough to fit the top of a percolator or funnel; it is bound with a wooden hoop, whose lower edge projects about half an inch below the under surface of the cover; to the wooden hoop is tacked a piece of moderately thin sheet-rubber, so that the cover, when completed, is like a drum-head, and when it is used to cover a percolator or funnel will make, by its elasticity, an air-tight covering.

B, is a funnel tube, so bent as to prevent evaporation or access of air. Through it, fresh menstruum or other liquid may be introduced into the percolator or funnel. A glass or metal tube answers the same purpose, and may be stopped with a cork. This tube may be adjusted by boring a hole in the wooden cover and punching a smaller hole in the rubber, so that it will fit snug around the tube.

C, is a rubber tube attached at one end to a glass tube in the cover (which passes through the rubber as heretofore described), and at the other end to a tube in the stopper of the receiving bottle. This tube allows the air to pass from the

receiving bottle into the percolator, and as the liquid fills the bottle the air is forced from it into the percolator or funnel.

D, is a rubber tube attached to the percolator that connects with a tube in the stopper of the receiving bottle, through which the percolate passes; if the lower end of the percolator is too large for the rubber tube, a perforated cork,

into which a glass tube is inserted, may be placed in the neck of the percolator for this purpose, as is directed in the pharmacopoeia process. By raising or lowering the percolator or the receiving bottle the flow of the percolate can be made more or less rapid, as it works on the principle of the syphon. The receiving bottle may be made of any wide