United States Dispensatory 1926
Compiled by Ivor Hughes
EXTRACTA. U. S. EXTRACTS.
"Extracts are either pasty or semi-solid masses, or dry, solid or powdered products prepared by exhausting drugs with appropriate solvents, carefully evaporating tho solution so obtained to the prescribed consistence
and adjusting the products to the fixed standards. An extract is intended to preserve the useful constituents of the drug in a concentrated, relatively uniform, permanent condition and in a form suitable for medication." U. S.
Extraits, Fr.; Extrakte, G.; Estratti, It.; Eitractos, Sp.
Extracts, as the term is employed in the Pharmacopeias, are solid preparations, resulting from the evaporation of the solutions of vegetable principles, obtained either by exposing a dried drug to the action of a solvent, or by expressing the juice from a fresh plant. A distinction was formerly made between those prepared from the infusions, decoctions, or tinctures, and those from the expressed juices of plants, the former being called Extracta, the latter Succi Spissati, but the distinction has been generally abandoned.
The composition of extracts varies with the composition of the plant, tho character of the solvent, and the mode of preparation. The object is generally to obtain as much of the active principle of the plant with as little of the inert matter as possible, though sometimes it may be desirable to separate two active ingredients from each other when their effects upon the system are materially different; this may be accomplished by employing a menstruum which, while it dissolves one, leaves the other untouched.
The proximate principles most commonly present in extracts are gum, sugar, starch, tannin, extractive, coloring matter, salts, and the peculiar principles of plants, to which, when an alcoholic solvent is employed, may usually be added resinous substances, fatty matter, and frequently more or less essential oil, gum and starch being excluded when the menstruum is pure alcohol.
Of these substances, as well as of others which, being soluble, are sometimes necessarily present in extracts, we have taken occasion to treat under various heads in this commentary. There is one, however, which from its supposed almost uniform presence in this class of preparations, and from the influence
it is thought to exert upon their character, deserves particular consideration in this place. We allude to extractive, or, as it is sometimes called, extractive matter.
It has long been observed that in most plant tissues there is a substance, soluble both in water and alcohol, which, in the preparation of extracts, undergoes characteristic changes during the process of evaporation, imparting to the liquid even if originally limpid, first a greenish, then a yellowish-brown, and ultimately a deep brown color, and becoming itself insoluble. This substance, originally called saponaceous matter by Scheele, afterwards received the more expressive name of extractive, derived from its frequent presence in extracts.
The most important property of extractive is its disposition to pass, by the influence of atmospheric air at a high temperature, into an insoluble substance. If a vegetable infusion or decoction be evaporated in the open air to the consistence of an extract, then diluted, filtered, and again evaporated, and the process repeated so long as any insoluble matter is formed, the whole of the extractive will ultimately be separated from the liquid, while the other ingredients may remain.
The name of oxidized extractive which has been given, to it is incorrect, and Berzelius proposed to substitute for it that of apothem, synonymous with deposit. According to Berzelius, apothem is not completely insoluble in water, but imparts a slight color to that liquid when cold, and is rather more soluble in boiling water, which becomes turbid upon cooling. It is still more soluble in alcohol, and is freely dissolved by solutions of the alkalies and alkaline carbonates, from which it is precipitated by acids. It has a great tendency, when precipitated from solutions, to unite with other principles, probably on account of its colloidal absorptive properties, and to carry them along with it, thus acquiring properties somewhat different according to the source from which it is obtained. In this way also, even when the extractive of a plant is itself medicinally inert, its conversion, into apothem may be injurious by causing a precipitation of a portion of the active principle, and in practical pharmaceutical operations this change should always, if possible, be avoided.
We shall treat of the subject under the several heads of
(1)
the extraction of the soluble principles from the plant;
(2)
the method of conducting the evaporation;
(3)
the proper condition of extracts, the changes they are liable to undergo, and the best method of preserving them.
1.
Extraction of the Soluble Principles.
There are two distinct modes of obtaining, in a liquid state, the principles which we wish to extract:
(1) by expression alone; (2) by the agency of a solvent, with or without expression.
By Expression.�This method is applicable to fresh vegetable tissues when they are very succulent and when other conditions are
favorable. It is not recognized by the U. S. but there are four preparations in the Br. in which expression of juice is employed. All plants cannot be usefully treated in this way, as many have too little juice to afford an appreciable quantity upon pressure, and of the succulent a considerable portion do not yield all their active principles with their juice. Succulent fruits, and various acrid and narcotic plants, are proper subjects for this treatment.
The plants should be operated upon, if possible, immediately after collection. Battley, of London, recommended that, if not entirely fresh, they should be revived by the immersion of the stalks in water for twelve or eighteen hours, and those only used which recover their freshness by this management. They should then be cut into pieces, and bruised in a stone mortar till brought to a pulpy consistence.
When the plant is not very succulent, it is necessary to add a little water during this part of the process, in order to dilute the juice. After sufficient contusion, the pulp is introduced into a linen or canvas bag, and the liquid parts expressed. Brande states that light pressure only should be employed, as the extract is thus procured greener, of a less glutinous or viscid consistence, and, in his opinion, more active than when considerable force is used in the expression. The juice thus obtained is opaque, and usually green, in consequence of the presence of chlorophyll, and of a portion of the undissolved vegetable tissues in minute division.
By heating the juice to about 71.1� C. the albumen contained in it coagulates, and, involving the chlorophyll and vegetable fiber, forms a greenish precipitate. If the liquid be now filtered, it becomes limpid and nearly colorless, and is prepared for evaporation. The clarification, however, is not absolutely necessary, and is generally neglected. Sometimes the precipitate carries with it a considerable portion of the active principle, in which case it should be subsequently incorporated with the juice, when the latter is reduced by evaporation to the consistence of syrup.
Chloroform or ether added to the expressed juices of plants enables them to be kept long without injurious change. Lepage, of Gisors, France, has kept the juice of belladonna preserved with ether more than ten years, and found it, at the end of that time, to yield an extract-identical in physical, chemical, and physiological properties with that obtained from the fresh juice.
2.
By Solution.
The solvent or menstruum to be employed in the preparation of an extract is dependent upon the physical characteristics of the drug and the nature of its constituents. The solvents commonly adopted are water or alcohol, or mixtures of these, in the proportions directed in the formulas. For the extraction of a few drugs, the addition of an acid or an alkali to the solvent is required. When alcohol is used as a solvent, it may be recovered by distillation. When a drug contains an oily constituent that is extracted by the menstruum, it becomes
necessary to adopt in the process of manufacture some method for the separation of this oil so that a permanent product of the proper consistence, dryness, or pulverulent form may be obtained." U. S.
The active principles of dried vegetable substances can be extracted only by means of a liquid solvent. The menstruum usually employed is either water or alcohol, or a mixture of the two. Water, on account of its cheapness, is always preferred, when circumstances do not strongly call for the use of alcohol. It has the advantage, moreover, that it may be assisted in its action if necessary by a higher degree of heat than the latter.
Tap water is often unfit for the purpose, in consequence of the quantity of its saline matter, which in some instances may exert an unfavorable influence on the active principle, and must always be left in the extract. Distilled water is preferred. Alcohol is employed when the principles to be extracted are insoluble or but slightly soluble in water, as in the case of the resins; when it is desirable to avoid in the extract inert substances, such as gum and starch, which are dissolved by water and not by alcohol; when the heat required to evaporate the aqueous solution would dissipate or decompose the active ingredients of the plant, as the volatile oils; when the reaction of the water itself upon the vegetable principles is injurious; and, finally, when the nature of the substance to be exhausted requires so long a maceration in water as to endanger spontaneous decomposition.
The aqueous solution requires to be quickly evaporated, as this fluid rather promotes than counteracts chemical changes, while an alcoholic tincture may be preserved unaltered for an indefinite period. An addition of alcohol to water is sufficient to answer some of the purposes for which the former is preferable, and the employment of both fluids is essential, when the virtues of the plant reside in two or more principles, all of which are not soluble in either of these menstrua. In this case it is usually better to submit the vegetable to the action of the two fluids successively than of both united.
Extracts obtained by the agency of water are called aqueous extracts; those by means of alcohol, undiluted or diluted, alcoholic or spirituous extracts. Sometimes the term hydro-alcoholic is applied to extracts obtained by the joint agency of alcohol and water. The methods of extraction are by infusion, decoction, maceration or percolation.
Chloroform is frequently used to saturate the water used in making aqueous extracts to prevent fermentation during percolation.
It is always desirable to obtain the solution in the first place as concentrated as possible, so as to prevent the necessity of long continued evaporation, which injures the extract. It is better, therefore, to incur the risk, both when decoction and infusion are employed, of leaving a portion of the active matter behind, than to obtain a very weak solution. When successive portions
of water are employed those which are least impregnated should be brought by evaporation to the strength of that first obtained before being mixed with it.
Acetic acid has been introduced into use as a menstruum in the preparation of extracts. It is supposed to be a better solvent of the active principles of certain substances than either water or alcohol alone. Experiments have shown that strong acetic acid (60 per cent.) is a powerful solvent for the active properties of various drugs, particularly those which contain volatile oils, and in many cases a 10 per cent, acetic acid is an excellent menstruum for making extracts; for these the name
acetract has been proposed.
(Proc. A. Ph. A., 1897, 416.) E. R. Squibb has used acetic acid largely for extracts. (West. Drug., 1897, 123.)
Ether also is now used to a considerable extent in the preparation of oleoresins which are a class of extracts. Having the property of dissolving volatile oil and resin, and of evaporating at a temperature insufficient to volatilize the oil, it is admirably adapted for the extraction of drugs the virtues of which reside in the two principles referred to. An ethereal tincture is first prepared by the process of percolation, and the ether is then allowed to escape by spontaneous evaporation, or distilled off at a very moderate heat. The oleoresinous extracts thus obtained are usually of a thick fluid or semifluid consistence. Several of them now rank among the official preparations, in the U. S. P., under Oleoresince. Acetone is another solvent used much for the same purpose as ether.
Powders�Fineness.
The fineness of vegetable drugs is expressed in this Pharmacopoeia by the following terms:
(1) coarse powder (No. 20), (2) moderately coarse powder (No. 40), (3) fine powder (No. 60), (4) very fine powder (No. 80). A powder to conform to any one of these specified terms must meet the requirement given below. In the preparation of ground or powdered drugs, no portion of the drug
shall. be rejected during milling or sifting unless specifically permitted under the official description of the drug. It is permissible, however, to withhold final tailings not exceeding 5 per cent. of the drug being powdered, which may be added in no greater percentage to other lots of the same drug in subsequent millings.
STANDARDS FOR UNIFORMITY OF FINENESS.
A coarse powder (No. 20) is one in which all of the particles will pass through a No. 20 standard mesh sieve and not more than 40 per cent, through a No. 60 standard mesh sieve. A moderately coarse powder (No. 40) is one in which all of the particles will pass through
a No. 40 standard mesh sieve and not more than 40 per cent, through a No. 80 standard mesb sieve. A fine powder (No. 60) is one in which all of the particles will pass through a No. 60 standard mesh sieve and not more than 40
per cent, through a No. 100 standard mesh sieve. A very fine powder (No. 80) is one in which of the particles will pass through a No. 80 standard mesh sieve."
The " standard sieves" referred to in the official description is intended to mean those that meet the standards of the U. S. Department of Commerce (Circular LC, 74, April 15,1924). This circular describes in detail the size of the opening, diameter of the wire and shape of sieve necessary to conform to Federal regulations; manufacturers may have their sieves certified by the Bureau of Standards by payment of a small fee. The meaning of the numbers adopted can be most readily explained by the following quotation from this Circular:
"Because of the wide range of openings in sieves now manufactured which is possible with a given number of meshes per unit length by the use of wires of different diameters, and the consequent confusion and uncertainty which arises in designating sieves by the number of meshes per unit length, it is recommended that all reference to mesh be avoided in the designation of the sieves, but that for convenience each sieve be given an abstract number which will indicate the approximate position of the sieve in the series.
The proper designation of a sieve is the size of the opening, supplemented by the wire diameter, but it is well recognized that few users of sieves will be able to carry the sizes of the various openings in mind without reference to a printed table. All that the users of sieves desire to know in general is that the sieves are ' standard,' that is, that they conform to established specifications, and therefore the only designation required is a simple one which will suggest the degree of fineness or coarseness of the material passing or retained upon any given sieve.
Such a designation is an abstract number which is approximately the number of meshes per linear inch. The advantage of such a designation is readily apparent. Thus the sieve, which has a 0.105 mm. opening, is given the number 140, which may be regarded simply as a fixed arbitrary number indicating that the sieve has approximately 140 meshes per inch. The fact that a sieve of nominal opening and wire diameter has actually 141.9 meshes per inch or 55.9 meshes per centimeter is of no importance; the number 140 merely indicates to those who are familiar with the old sieves what order of separation this sieve would give in testing any graded material. It is urgently recommended that all users of sieves in the future designate these standard sieves by these arbitrary numbers approximately the mesh per inch, and that the manufacturers mark and list the sieves in this manner, together with the size of the openings and the wire diameters in both millimeters and inches." Circular, U. S. Bureau of Standards.
" METHOD FOR DETERMINING UNIFORMITY OP FINENESS.�For determining uniformity of degree of fineness of a powdered vegetable drug, the following process shall be used, employing standard testing sieves which meet the
requirements of the Bureau of Standards, U. S. Department of Commerce. For coarse and moderately coarse powders, place from 25 to 100 Gm. of the powder to be tested upon the proper standard testing sieve with a tightly fitting receiving pan and cover. Shake the sieve in a rotary horizontal direction and vertically by tapping on a hard surface for not less than twenty minutes or until no appreciable number of particles pass through the sieve. Weigh accurately the amount remaining on the sieve and in the receiving pan and calculate to per cent. In the case of fine or very fine powders, proceed as for coarse or for moderately coarse powders, but shake the sieve for at least thirty minutes or until no appreciable number of particles pass through the sieve.
In the case of oily or other powders which tend to clog the openings, the screen should be carefully brushed at intervals during the test. In the ease of powders which tend to form lumps, such lumps �should be carefully disintegrated during the sifting test. In all cases care must be taken not to increase the fineness of the powder during the process of sieve testing.
" Mechanical testing machines which impart a rotating and tapping effect to the testing sieves may be employed for making the tests. In all cases care must be taken to see that the separation is complete before the weighings are made.
Percolation and Maceration.
Percolation, as directed in this Pharmacopoeia, consists in subjecting a comminuted substance or a mixture of substances, contained in a vessel called a percolator, to the solvent action of successive portions of a liquid termed the menstruum in such a manner that the liquid, as it traverses the powder in its descent to the receiver, shall extract the soluble constituents, 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. In preparations which direct the process of percolation, wherever the expression ' until the drug is exhausted' or a similar phrase occurs, it is to be understood that the term ' exhausted' means that point at which the valuable constituents have been as completely extracted as is practicable, and this must be determined by the judgment and experience of the operator.
" Percolators.�The following statement with regard to percolators and the process of percolation is given in order to illustrate a method of percolation. It is not intended to be compulsory and it is permissible for manufacturers and others to modify the process to suit their needs. 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 wider toward the orifice, so that a perforated cork, bearing a short glass tube, may be tightly wedged into it. The glass tube, which must not project 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 (when it is desired to interrupt the percolation) the rubber tube may be so suspended that its orifice shall be above the surface of the menstruum in the percolator, a rubber band or wire loop holding the tube in position.
The shape of the percolator should be adapted to the nature of the drug to be operated upon. For drugs which are apt to swell, particularly when a weak 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 likely to swell, particularly if difficult to exhaust, also 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, the drug should not occupy more than two-thirds of the height of the percolator. The percolator is best constructed of glass, but, unless otherwise directed, may be made of any suitable material not affected by the drug or menstruum. Metallic percolators are required for hot percolation. The percolator is prepared for percolation by gently pressing a small tuft of purified cotton into the neck, and this may then be moistened by pouring a few drops of menstruum upon the cotton, to facilitate the passage of the first portion of percolate, which is often very dense.
" The Process.�The substance to be percolated, of the fineness directed in the formula, and thoroughly air-dried before it is weighed, is put into a suitable dish, sufficient menstruum is poured on, and the powder stirred until it is uniformly moistened. The moist powder is then passed through a sieve. Coarse powders 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 fifteen minutes to several hours, unless otherwise directed.
After maceration, the moist powder is removed from the percolator, and then returned in suitable portions, pressing each portion, with 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, permit firmer packing of the powder than weaker menstrua.
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 disc of filter paper, held in place by a layer of washed sand or a glass stopper or percolator weight, and a sufficient quantity of the menstruum is 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, 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 for maceration 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 tared, if the percolate is to be weighed. By raising or lowering this receiver the rapidity of percolation may be increased or decreased as may be desirable. A layer of menstruum must constantly be maintained above the powder, 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 described, and the liquid poured on until all has passed from the surface, when immediately a sufficient quantity of the directed menstruum should be poured on to displace the retained liquid and obtain the prescribed quantity.
" Repercolation or Fractional Percolation.� Authority is given to employ, where it may be applicable, the process of repercolation, without change of the initial menstruum or the process of fractional percolation, described in Type Process C for
fluidextracts.
"Rate of Flow.�The success of the process of percolation largely depends upon the regulation of the flow of the percolate; if this is too rapid, incomplete exhaustion will result, but if too slow, valuable time is wasted and considerable loss of menstruum occurs from evaporation. For fluidextraets using 1000 Gm. of powder, the rate of flow should not exceed ten drops a minute; for official quantities of tinctures and
preporations of about the same strength, twenty drops a minute, and the word " slowly " throughout the text is understood to mean a rate of flow corresponding to this. The proper rate of flow should vary with the quantity and character of the drug employed and the density of the menstruum.
" Maceration.�Percolation is not suitable for exhausting some drugs, and for such the process of maceration is employed. The tinctures of asafetida, sweet orange, and tolu are illustrations. Maceration should be conducted preferably at a temperature of from 15� to 20� C. Specific directions will be found in the monographs." U. S.
For an account of E. R. Squibb's process of repercolation, see Fluidextracta.
Large scale production enables the pharmaceutical manufacturer to employ vacuum stills for recovering the solvents and enabling concentration to be effected at temperatures which are not injurious to the principles involved.
2. Mode of Conducting the Evaporation.
"In the preparation of extracts, the concentration of the liquid extractions is to be completed without delay, and undue exposure to heat must be avoided. The limit of temperature for the evaporation, as stated in the formulas, should not be exceeded. In the manufacture of extracts on a large scale, apparatus for distilling and evaporating under reduced pressure should be used. It is also important that the residue be frequently stirred in order to hasten the evaporation and to obtain a uniformly smooth product. In the preparation of powdered extracts, it is necessary to use solvents that will extract the active principles of the drug and only a minimum amount of inert substance.
The drying of the soft extract can be greatly facilitated by spreading it upon plates of glass or tinned metal and exposing it to currents of warm dry air. Powdered extracts must be thoroughly dried, powdered, intimately mixed with the diluent, and carefully preserved as directed below." U. S.
In evaporating the solutions, attention should always be paid to the fact that the extractive matter is constantly becoming insoluble at high temperatures with the access of air, and that other chemical changes are going on, sometimes not less injurious than this, while the volatile principles are expelled with the vapor. The operator should, therefore, observe two rules:
(1)
to conduct the evaporation at as low a temperature as is consistent with other objects;
(2)
to exclude atmospheric air as much as possible, and, when this cannot be accomplished, to expose the liquid the shortest possible time to its action.
The injurious influence of atmospheric air is much greater at the boiling point of water than at a less heat, even allowing for the longer exposure in the latter case, and therefore a slow evaporation at a moderate heat is preferable to the more rapid effects of ebullition.
First, however, it is proper to observe that decoctions generally let fall, upon cooling, a portion of insoluble matter, and it is a question whether this should be rejected, or retained so as to form a part of the extract. Though it is undoubtedly in many instances inert, as in that of the insoluble substance formed during the decoction of certain vegetable substances, yet, as it frequently also contains a portion of the active principle which a boiling saturated solution necessarily deposits on cooling, and as it is difficult to decide with certainty when it is active and when otherwise, the safest plan, as a rule, is to allow it to remain.
The method of evaporation formerly resorted to in the case of aqueous solutions is rapid boiling over a fire. This method has been entirely superseded by the use of steam in connection with reduced pressure. The use of the vacuum kettle or evaporator has become very general in this country, as it requires a smaller consumption of fuel, and the heat imparted to the liquid, while sufficient to evaporate it, may be considerably less than 100� C.
A former plan of evaporation, though slow, was to place the liquid in a broad, shallow vessel, exposed in a stove or drying room to a temperature of about 37.8� C., or a little higher, taking care that the air have free access in order to facilitate the evaporation.
In the concentration of alcoholic solutions, distillation should always be performed, as not only is the atmospheric air thus excluded, but the alcohol is recovered, if not absolutely pure, certainly fit for the purpose to which it was originally applied.
When the decoction or infusion and the tincture of the same vegetable have been made separately, they should be separately evaporated to the consistence of syrup, and then mixed together while they are of such a consistence as to incorporate without difficulty. The object of this separate evaporation is that the spirituous extract may not be exposed to the degree of heat, or lengthened action of the air, which is necessary in the ordinary mode of concentrating the infusion or decoction.
In every instance, care should be taken to prevent any portion of the extract from becoming dry and hard on the sides of the evaporating vessel, as in this state it will not readily incorporate with the remaining mass. The heat, therefore, should be applied to the bottom and not to the sides of the vessel.
" Alkaloidal standards have been adopted for those extracts that can be reliably assayed. Assay methods are directed for the determination of their strengths and to provide for their standardization. When necessary, an inert diluent is directed to reduce the product to the standard. In the official formulas, glucose is directed in most instances as the diluent for the pilular extracts, and dried starch for the powdered extracts. It is permissible, however, for the manufacturer to use as inert
diluents, for the former, a sub-standard extract of the same drug; for the latter, sucrose, lactose, powdered glycyrrhiza, magnesium carbonate, or the finely powdered, dried drug or marc from which the respective extract was made.
Before admixture the diluent may be colored by the addition of chlorophyll, caramel or other harmless coloring to simulate the color of the extracts. For the convenience of the prescriber, the standards of strength for the extracts have been adjusted wherever possible, so that each bears a definite relation to that of the respective drug of average strength. A statement of the standard adopted accompanies each formula." U.
S.
C. H. LaWall has prepared a valuable table giving the yield of extract by various drugs. (Proc. A. Ph. A., 1897, 414.) For methods of assay, see various official processes.
" The pasty or semi-solid extracts are designated 'pilular extracts' because they are extensively used in pill masses. They are also used in ointments, and to facilitate their use in these preparations, the degree of concentration is directed to be that of a ' pilular consistence.' In these, an excess of moisture is to be avoided and the proper pliability and consistence may be maintained by the addition of a small amount of glycerin. Pilular extracts should be protected from exposure to sunlight, air, and moisture, by being kept in tightly-covered glass or earthenware containers, and should be stored in a cool, dark place.
" Powdered extracts differ from pilular extracts in that they are dry and prepared either as fine or granular powders. They are more generally used than pilular extracts because they can be more accurately weighed, more easily dispensed, and more conveniently preserved. These should be preserved in tightly-stoppered, small, wide-mouthed, amber-colored bottles, and stored in a cool, dry place." U. S.
Extracts of the pilular character, in order that they may keep well, should be placed in glazed earthenware, glass, or porcelain jars, and completely protected from the access of the air. This may be effected by covering their surface with a layer of melted wax, or with a piece of paper moistened with strong spirit, then closing the mouth of the vessel with a cork, spreading wax or rosin over this, and covering the whole with leather or a piece of bladder. The application of alcohol to the surface has a tendency to prevent mouldiness.
Should the extract become too moist, it may be dried by means of a water bath; should it, on the contrary, be too dry, the proper consistence may be restored by softening it in the same manner and incorporating with it a little distilled water.
When extracts which are too soft are subjected to a moderate temperature, fermentation or molding may set in; E. Cocardas describes the various forms of micro-organisms which are found in such extracts, and concludes that the ferment causes them to undergo changes similar
to those effected by heat�via., the absorption of oxygen and the disengagement of carbon dioxide. (P. J. 1886, p. 590.) ,,
The addition of a little glycerin has been suggested to prevent the hardening of extracts; the U. S. directs the addition of glucose in the pilular extracts which will have a like effect. The U. S. VIII officially recommended the addition of glycerin. It is preferable to add a definite weight of the glycerin to the percolate. If it were added to the menstruum, owing to the variation in the yield of extracts from plants, some would be too soft, and at another time, in the case of a large yield of extract, the quantity of glycerin would be insignificant.
Extracts from recent plants should be prepared at the season when the plant is medicinally most active; a good rule is to prepare them once a year; but the demand for extracts from fresh drugs has almost entirely ceased, as it has been found that properly dried drugs yield extracts of uniform strength.
Powdered extracts are always prepared by vacuum evaporation and they are stabilized by incorporating some inert material as starch, lactose or magnesium carbonate to prevent absorption of moisture and caking. They must be kept in tightly stoppered containers.
A. B. Lyons, of Detroit (1898), has introduced scale extracts. These do not, as a class, bear a definite relation to the drug; they are assayed, however, and acacia is used as a means of preserving their dry condition; they are easily pulverized, and are very convenient for dispensing.
