Extracta et Extracta Fluida.—Extracts and Fluid Extracts.

Related entries: Alcohol.—Alcohol

Fluid Extracts - National Formulary General Directions: General Processes - The Menstruum Contains No Glycerin - The Menstruum Contains Glycerin - Fractional Percolation - U. S. P. General Directions for Percolation: Fineness of Powder - Percolation - Repercolation - The Percolator - Solid extracts - Aqueous Extracts - Alcoholic Extracts - Hydro-alcoholic Extracts - Inspissated Juices

Other tomes: USDisp - USDisp - BPC - AJP1871 - AJP1883 (4 parts) - AJP1885

Fluid and Solid Extracts.—Formerly these preparations were separated into two classes and were considered in different sections of the Pharmacopoeia. At present they are arranged therein successively in alphabetical order, in one general class. We shall thus consider them, first prefacing the formulae by appropriate introductory remarks.

Extracta Fluida.—FLUID EXTRACTS. These are concentrated alcoholic liquids, and have the advantage over solid extracts in being prepared with less evaporation, and consequently less heat, whereby their activity is not so liable to impairment. With some drugs in which the medicinal virtues depend entirely upon a volatile fluid or evanescent substance, and can not be reduced to a solid extract or a dry condition, the fluid extract or a fluid representative, presents the only rational mode of drug administration. The established strength of fluid extracts preceding the U. S. P. of 1880, was 1 troy ounce of drug to 1 fluid ounce of the finished fluid extract. The present strength, with few exceptions, is 1000 grammes of the drug to 1000 cubic centimeters of the finished fluid extract. This deviation from the original strength is so little as to be of no consequence when taken in connection with the variation in drug quality and the personal equations of the operator and patient. For all practical purposes, there is no distinction between the therapeutical values of fluid extracts made by the old or the new pharmacopoeial standards. The menstruum employed in the preparation of fluid extracts varies according to the character of the energetic constituents of the plant; thus, many agents require only enough alcohol to preserve them, while those containing oils and resins require increased alcohol according to the degree of solubility in this menstruum. Great care and attention are required in making these preparations, from the fact that too high a temperature or too long an exposure to the action of the atmosphere frequently tends to decompose and render them worthless. One trouble relative to some of the fluid extracts is their natural tendency to subsequent decomposition; the result being the formation of precipitates that often contain valuable medicinal agents. But it does not necessarily follow that the result of decomposition is always accompanied by the formation of sediments; in many cases liquids lose their therapeutic value and still remain comparatively transparent.

The terms Essential tinctures, Concentrated tinctures, and Saturated tinctures have been applied to preparations similar to or identical with fluid extracts, but they have long since been displaced by the name fluid extract, and are practically obsolete. The U. S. P. contains an extensive list of fluid extracts, but not as extensive as the catalogues of medicinal manufacturers. To these formulae we have added many others, but to give formulae for the entire line of commercial fluids is impracticable. The Pharmacopoeia contains general directions for percolation that can be easily adapted to unofficial extracts, the operator selecting the menstruum that is applicable to each drug. In addition to this, the National Formulary contains explicit general directions for making many unofficial fluid extracts, which general directions may appropriately be introduced before the official processes, these being given in detail by us. In our opinion, both these general methods may be improved upon, in many cases, by evading evaporation altogether. The official preparations are in accordance with the metric system, but those introduced from other sources are given in troy ounce and fluid measure.

National Formulary General Directions.—EXTRACTA FLUIDA (N. F.), Fluid extracts. Formulary number, 135: "The fluid extracts for which formulas are given in this formulary, are intended to be of the same strength as the fluid extracts of the U.S.P., which directs that one hundred cubic centimeters (100 Cc.) [3 fl℥, 183♏︎] of fluid extract shall be obtained from one hundred grammes (100 Gm.) [3 ozs. av., 231 grs.] of the drug."

GENERAL PROCESSES.—"The fluid extracts of this formulary are to be prepared according to one of the following two processes, the particular one to be employed being designated in each case. These two processes are necessary because, in the preparation of some fluid extracts, two fluids are successively used, the first containing glycerin, and being in definite proportion to the drug used, while the second is free from glycerin, being intended for the exhaustion of the drug and subsequent evaporation. Accordingly, these menstrua are designated as Menstruum I (containing glycerin), and Menstruum II (containing no glycerin). As an alternative to either of these processes, a third process, dependent upon Fractional Percolation may be used. In this the use of heat is avoided, and it involves the use of only one kind of menstruum, even in the case of drugs for which two different menstrua (I and II) are prescribed in this formulary. In the case of the latter, a sufficient quantity of Menstruum I must be prepared to serve throughout the process."

Ɣ PROCESS A. THE MENSTRUUM CONTAINS NO GLYCERIN.—"Moisten one thousand grammes (1000 Gm.) [2 lbs. av., 3 oz., 120 grs.] of the drug with a sufficient quantity of the prescribed menstruum to render it distinctly damp, and to maintain it so after several hours' maceration in a well-covered vessel. When the drug has ceased to swell, pack it in a suitable percolator, pour a sufficient quantity of the menstruum on top, and when the percolate begins to drop from the orifice, close the latter, cover the percolator, and allow the contents to macerate 24 hours. Then permit the percolation to proceed. Receive the first eight hundred end seventy-five cubic centimeters (875 Cc.) [29 fl℥, 282♏︎] of the percolate separately and set it aside. Then continue the percolation with the same menstruum until the drug is practically exhausted. Evaporate this second portion—at a temperature sufficiently low to prevent the loss of any important volatile constituent—to a soft extract, and dissolve this in a sufficient quantity of menstruum so that when this is added to the reserved portion, the product will measure one thousand cubic centimeters (1000 Cc.) [33 fl℥, 391♏︎]. Allow the fluid extract to stand a few days, or longer if convenient, and filter, if necessary."

Ɣ PROCESS B. THE MENSTRUUM CONTAINS GLYCERIN.—"Moisten one thousand grammes (1000 Gm.) [2 lbs. av., 3 ozs., 120 grs.] of the drug with a sufficient quantity of Menstruum I to render it distinctly damp and to maintain it so after several hours' maceration in a well-covered vessel. When the drug has ceased to swell, pack it in a suitable percolator and pour the remainder of Menstruum I on top. When this has just disappeared from the surface, follow it by a sufficient quantity of Menstruum II. As soon as the percolate begins to drop from the orifice, close the latter, cover the percolator, and allow the contents to macerate during 24 hours. Then permit the percolation to proceed. Receive the first eight hundred and seventy-five cubic centimeters (875 Cc.) [29 fl℥, 282♏︎] of the percolate separately and set it aside Then continue the percolation with Menstruum II, until the drug is practically exhausted. Evaporate this second portion—at a temperature sufficiently low to prevent the loss of any important volatile constituent—to a soft extract, and dissolve this in a sufficient quantity of Menstruum II, so that when this is added to the reserved portion, the product will measure one thousand cubic centimeters (1000 Co.) [33 fl℥, 391♏︎]. Allow the fluid extract to stand a few days, or longer, if convenient, and filter, if necessary."

PROCESS C. FRACTIONAL PERCOLATION.—"Take of the drug, in powder of the prescribed fineness, one thousand grammes (1000 Gm.) [2 lbs. av., 3 ozs., 120 grs.], and divide it into three portions of five hundred grammes (500 Gm.) [1 lb. av., 1 oz., 279 grs.], three hundred and twenty-five grammes (325 Gm.) [11 ozs. av., 203 grs.], and one hundred and seventy-five grammes (175 Gm.) [6 ozs. av., 76 grs.], respectively. Moisten the first portion of the drug, five hundred grammes (500 Gm.) [1 lb. av., 1 oz., 279 grs.] with the menstruum and percolate in the usual manner. Set aside the first one hundred and seventy-five cubic centimeters (175 Cc.) [5 fl℥, 440♏︎] of percolate, and continue until fifteen hundred cubic centimeters (1500 Cc.) [50 fl℥, 346♏︎] more of percolate have passed, which must be received in several portions, so that the more concentrated will be separate from the last weak percolate. Then moisten the second portion of the drug, three hundred and twenty-five grammes (325 Gm.) [11 ozs. av., 203 grs.] with the more concentrated percolates received during the preceding operation, after the first one hundred and seventy-five cubic centimeters (175 Cc.) [5 fl℥, 440♏︎] have passed, and percolate again in the usual manner, using the several reserved percolates, successively, as menstrua. Set aside the first three hundred and twenty-five cubic centimeters (325 Cc.) [10 fl℥, 475♏︎], and continue the percolation until six hundred and fifty cubic centimeters (650 Cc.) [21 fl℥, 470♏︎] more have passed, which should also be received in several portions. Finally, moisten the third portion of the drug, one hundred and seventy-five grammes (175 Gm.) [6 ozs. av., 76 grs.] with the most concentrated of the last reserved percolates, and proceed as directed for the second portion. Collect five hundred cubic centimeters (500 Cc.) [16 fl℥. 435♏︎], of percolate, and mix with the two portions (325 and 175 Cc.) previously set aside, so as to make one thousand cubic centimeters (1000 Cc.) (33 f1℥, 391♏︎] of fluid extract. Note.—If this method is applied to drugs for which Process B is directed, use a sufficient quantity of Menstruum I to obtain the required quantities of percolate, and omit the use of Menstruum II."

U. S. P. General Directions for Percolation.—FINENESS OF POWDER. "The fineness of powder is expressed, in the Pharmacopoeia, either by descriptive words (generally so in the case of brittle or easily pulverizable substances), or in terms expressing the number of meshes to a linear inch of the sieve through which the powder will pass. The corresponding values, in terms of metric measures of length, are added below in parentheses, but it has not been deemed advisable, in this revision, to substitute them in the text of the Pharmacopoeia for those at present in use.

These different forms of expression correspond to each other as follows:

"In certain cases, powders of a different degree of fineness (e.g., No. 30, No. 12) are directed to be taken.

"When a substance is directed to be in powder of a limited degree of fineness, as specified by the number of meshes to the linear inch in the sieve, not more than ¼ of the powder should pass through a sieve having 10 meshes more to the linear inch"—(U. S. P.).

Ɣ PERCOLATION.—"The process of percolation, or displacement, directed in this Pharmacopoeia, consists in subjecting a substance or a mixture of substances, in powder, contained in a vessel called a percolator, to the solvent action of successive portions of a certain menstruum in such a manner that the liquid, as it traverses the powder in its descent to the receiver, 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 nearly free from color, odor, and taste, other than those of 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 funnel-end should be rather short, and should gradually and regularly become narrower towards 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 the outer edge of the orifice. The glass tube, which must not project above the inner surface of the cork, should extend from 3 to 4 Cm. (about 1 ¼ to 1 ½ inches) 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 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, but, unless otherwise directed, may be made of any suitable material not affected by the drug or menstruum.

"The percolator is prepared for percolation by gently pressing a small tuft of cotton into the neck above the cork, a thin 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 this into the percolator. It is then shaken down lightly and allowed to remain in that condition for a period varying from 15 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 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 be accurately observed, the menstruum will penetrate the powder equally until it has passed into the rubber tube and has reached, 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 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 receiver the rapidity of percolation may be increased or decreased as may be desirable, care being taken, however, that the rate of percolation, unless the quantity of material be largely in excess of the pharmacopoeial quantity, shall not exceed the limit of 10 to 30 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 of a 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"—(U. S. P.).

REPERCOLATION.—"Authority is given to employ, in the case of Fluid Extracts, where it may be applicable, the process of repercolation, without change of the initial menstruum"—(U. S. P.).

In addition to the foregoing, we will reproduce the following remarks from our 1881 supplement, wherein we consider in detail some points that may prove of use.

Other tomes: King's (tinctures) - AJP1883 (percolator) - AJP1883 (filtering) - AJP1883 (more tinc)

Ɣ THE PERCOLATOR should be of glass where moderate amounts of material are operated upon. Large quantities require tin or wood. In all cases they should be nearly cylindrical, slightly conical, and of such diameter that the powder would occupy at least 1 foot in perpendicular height when properly packed.

To Prepare the Percolator for Percolation.—Provide a tapering cork which will perfectly close the exit or discharging aperture, so that when the percolate appears, the flow may be at once arrested. Then slice one side of the cork wedge-shape, commencing at the small end, as shown in Fig. 113, care being taken that the cut does not extend beyond that part of the cork which closes tightly the exit of the percorator. Now, place a layer of cotton upon the bottom of the percolator, as shown by Fig. 112, A; and, if convenient, a smooth layer of silver sand upon the cotton.

The 16 troy ounces of powder intended for percolation should, as soon as it is ready, be placed in the percolator, about one-fourth its bulk at a time; the surface should be smoothed after each addition, and then pressed as directed, for each drug. It is necessary that the pressure be even throughout the entire mass, otherwise the liquid will select the more porous portions, and thus yield a defective percolation.

It is best to select some flat circular body or disk to use in pressing the powder, and for this purpose a circular stick of wood with a smooth end, in thickness about two-thirds the diameter of the inside of the percolator, answers very well, care being taken that all portions of the surface of the powder are submitted alike to the pressure.

By moderately, we understand the pressure of from 5 to 10 pounds; firmly, from 15 to 20 pounds; and very firmly, the convenient pressure of one hand, not to exceed 50 pounds. Some little practice with a pair of spring balances will enable the operator to form an idea of the pressure required. Dr. E. R. Squibb, in New Remedies, Jan., 1879, suggests "moderately" as a pressure of 45 pounds; firmly, 60 pounds; and hard, 75 pounds, or more. This will answer very well for large quantities, or where the pressure is exerted upon a considerable surface, as with "both hands," thus, in reality, reducing the actual pressure upon each square inch to, or below, that given by us, which is intended to apply to only 16 troy ounces of material. We are assured, from experience, that the operator will work to disadvantage if a greater pressure is employed than advised by us. Having the powder properly packed, and the surface smooth, cut a piece of filtering paper to fit closely within the percolator, and place it upon the surface of the powder, and upon this place a few fragments of glass to retain it in position. Then add the menstruum, as directed, and cover the percolator with a plate or disk of ground glass, and, when the percolate appears, close the orifice tightly with the cork, and proceed according to the process given for making the particular extract. It must be observed that the cork is not inserted in the exit of the percolator until the percolate has appeared. When the period of maceration is over, gently twist and slowly withdraw the cork until the slit previously cut upon its side permits the liquid to pass in drops, without running in a stream.

Extracta.—EXTRACTS (solid extracts). When an infusion, decoction, or tincture is reduced to a soft, solid mass by evaporation, either spontaneous or artificial, it is termed an Extract. If it be prepared from a decoction or infusion it is called a Watery, or Aqueous Extract; if from an alcoholic tincture, it forms an Alcoholic Extract; if both water and spirit are used in preparing it, it is termed a Hydro-alcoholic Extract; if ether, wine, or acetic acid be the menstruum from which it is made, it is called Ethereal, Vinous, or Acetous Extract, according to the fluid used. The most important point in the manufacture of extracts is to employ as a solvent a liquid that will take up the medicinal constituents of a remedy, and but little, if any, of its inert portions. The constituents of plants not desirable to extract are gum, coloring matters, saccharine matter, etc., and as these are soluble in water, and are usually less soluble in alcohol, in most cases alcohol is a better medium for obtaining the active principles. The best solvent to abstract the medicinal virtues of plants will be that fluid in which they are the most readily dissolved: thus, resins, oils, oleoresins, etc., require alcohol, and, occasionally ether; alkaloidal principles occasionally require acidulated fluids; bitter extractive requires water; and some plants contain constituents that require two or more solvents, employed successively, the several residual extracts being mixed after, they have all been thus obtained. In the preparation of an extract, the operator should previously acquaint himself with the nature of the principles contained in the drug, their solubility, their relations to heat and air, their volatility, etc., so that he may adopt the menstruum best calculated to remove the greatest amount of active matter, and should control the evaporation, so that this may not be injured by heat, or lost by volatilization.

Probably no class of remedial agents requires more care in their preparation; for, if an extract be improperly prepared, either by employing a wrong solvent, or too much heat, it is not to be relied upon by the physician. In many cases the extract must be evaporated in vacuo, which operates against the pharmacist, for he can not afford this expensive apparatus. On this account it is very difficult for druggists or physicians to compete in this direction with manufacturers.

In some cases glycerin is useful as a part of the menstruum, both as a solvent and to prevent subsequent drying of the extract. The U. S. P. contains the following directions for such preparations: "When it is desired to preserve a solid extract (for instance, of gentian, taraxacum, etc.) in a plastic condition, suitable for making pills, or for other purposes, it is recommended that there be incorporated with it, after it has been evaporated to the proper consistence, and while it is still warm, 10 per cent of its weight of glycerin"—(U. S. P.).

Ordinarily, the plan adopted is, to obtain the juice, or tincture, of the plant, gently heat it to coagulate albuminous substances, filter or strain it, and then evaporate at a temperature ranging between 32.2° and 93.3° C. (90° and 200° F.), being careful not to raise it to the boiling point. A high temperature, as well as atmospheric action, will impair the efficiency of the preparation.

In forming the solution for aqueous extracts, soft water, as free from foreign matters as possible, should be employed. Clean rain water, or the water from some of our lakes or rivers, will be found to answer quite as well as water which has been distilled. The articles to be acted upon by the fluid should be ground, but not too finely, the degree of fineness depending upon the substance used, and the resulting liquid should be obtained from them by the process of displacement. The evaporation should be conducted at as low a temperature, and as quickly as the nature of the solution will admit, using a broad, shallow dish. Long continued evaporation by heat, under exposure to the atmosphere, is as detrimental to an extract as a boiling heat, hence the solutions should be procured in as concentrated a form as possible. And in those instances where different solutions are obtained, the weaker ones should be the first evaporated; by this means, the more concentrated liquids will not be injured by too long an exposure to heat.

When alcohol or ether is used in the preparation of extracts, it will be best to distill these fluids, not only for the purpose of saving them, but likewise to prevent the extracts from being impaired by atmospheric influence; a vacuum apparatus, however, will be superior to ordinary distillation, as these fluids way be evaporated at a much lower temperature. Hydro-alcoholic extracts are best made by first forming an alcoholic extract from the plant, then an aqueous extract, and combining the two while hot. Ethereal extracts are usually of a semi-fluid consistence. By means of Mohr's continuous displacing apparatus, as the percolated tincture falls into the receiver, the ether is driven off to pass again through the articles, and thus continues until all their strength is exhausted; the whole process of tincturing and forming an extract being thus performed at the same time. Extracts should be kept in glass, stone, or earthenware vessels, and be guarded as much as possible from the action of air and light, by covering them closely. The modes of preparing extracts are as follows:

Ɣ 1. Aqueous Extracts.—Take of the leaves, root, bark, or other part of the plant employed, in powder more or less fine, 1 pound; water, a sufficient quantity. Mix the leaves, or roots, etc., with half their weight of clean, soft water; in 12 hours put the whole into a displacement apparatus, and exhaust it by adding water to it from time to time, until the liquid which passes no longer contains any of the virtues of the plant, or part of it employed. Expose this filtered infusion to a temperature of 100° C. (212° F.), then strain it, and evaporate it in the vapor-bath at a temperature not to exceed 48.8° C. (120° F.), to the due consistence; or, the evaporation may be conducted in a vacuum apparatus.

Ɣ 2. Alcoholic Extracts.—Take of the leaves, root, bark, or other part of the plant employed, in powder more or less fine, 1 pound; alcohol (or diluted alcohol), water, of each, a sufficient quantity. Mix the leaves, or root, etc., with half their weight of alcohol, or enough to thoroughly moisten them; in 24 hours put the whole into a displacement apparatus, and exhaust by adding alcohol to it from time to time, until 4 pints of tincture have been obtained. Then add clean, soft water, and continue until the liquid which percolates causes a slight turbidness of the previously filtered liquor, as it drops into it. (The object of adding the water toward the latter part of the process is to remove the alcohol absorbed by the powder; and as soon as this is affected, and the water commences to percolate, it causes a turbid condition of the filtered alcoholic fluid immediately around the drops as they fall into it.) Place the filtered liquor in a suitable vacuum apparatus, and remove the alcohol, and then, if necessary, evaporate the residue in the vapor-bath at a temperature not to exceed 48.8° C. (120° F.) to the due consistence; or, which is much better, the whole process of evaporation may be carried on in a vacuum apparatus.

3. Hydro-alcoholic Extracts.—Take of the leaves, root, bark, or other part of the plant employed, in powder more or less fine, 1 pound; alcohol, 90 per cent, water, of each, a sufficient quantity. Mix the leaves, or roots, etc., with half their weight of alcohol, or enough to thoroughly moisten them; in 24 hours put the whole into a displacement apparatus, and exhaust by adding alcohol to it from time to time, until it passes off without any taste of the article employed. Remove the greater part of the alcohol from this filtered tincture, and evaporate the remainder to the proper consistence in one of the ways named in the preceding pages; that in vacuo being the best.

To the powder in the displacement apparatus, add gradually water, a sufficient quantity, until the liquid which passes no longer contains any of the virtues of the plant employed. Expose this filtered infusion to a temperature of 100° C. (212° F.), then strain it, and evaporate it in the vapor-bath to the due consistence. Mix the alcoholic and aqueous extracts thus obtained, while each is hot, and stir constantly until cold. With a few exceptions, alcoholic extracts are found to be superior to any others.

Any variation from the above process, in the preparation of the following extracts, will be explained under its appropriate head.

INSPISSATED JUICES are solid extracts made by evaporating the juices of fresh plants in vacuo. For an example see Extract of Taraxacum.

King's American Dispensatory, 1898, was written by Harvey Wickes Felter, M.D., and John Uri Lloyd, Phr. M., Ph. D.