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of crystallization are termed amorphous. Every crystallizable body assumes its own peculiar form, or some other form directly derived from or related to it. The process of crystallization is effected (1) by fusion and partial cooling, as in the cases of some metals and Sulphur; (2) by sublimation, as Benzoic Acid, Mercuric Chloride, etc.; (3) by deposition from hot saturated solutions while cooling; (4) by deposition from a solution during evaporation; (5) by deposition caused by passing a galvanic current through the solution; (6) by precipitation, as in the case of the Mercuric Iodide; (7) by the addition to the solution of a substance having a strong affinity for water, as in the adding of Calcium Chloride to an aqueous solution of Sodium Chloride, or Alcohol to a solution of Potassium Nitrate, or to an aqueous syrup. In a few cases amorphous solids may crystallize without undergoing liquefaction, as Sulphur, Barleysugar, Iron or Brass wire. The methods most frequently employed are those by deposition from supersaturated solutions, and by deposition during evaporation. The more slowly the process is carried on the larger and more regular will be the crystals. The process is facilitated by use of foreign bodies as nuclei around which the crystals are deposited; a familiar instance being the thread in the centre of a mass of rock-candy.
The Water of Crystallization is the H2O with which most substances combine in the act of crystallization, and the number of molecules thereof differs for each body and for the same body frequently under different conditions. Exsiccation is the driving off of this combined water by heat, the crystals assuming thereby the form of a dry powder. Eflorescence is a similar process occurring spontaneously on exposure of the crystals to the air, the effloresced portion appearing as a dry powder on the surface of the crystals. Deliquescence, on the other hand, is the act of absorbing water from the atmosphere, a property possessed by some substances which are therefore said to be hygroscopic.
Granulation is a process of reducing a coarsely crystalline substance to a granular powder by dissolving it in water and evaporating the solution with constant stirring until the product becomes perfectly dry. Many salts are thus treated for convenience in dispensing, as the Bromide, the Iodide, the Carbonate and the Citrate of Potassium. Sulphate of Iron, though generally dispensed in the exsiccated powder, may be granulated into minute crystals by filtering an aqueous solution of it into alcohol.
Dialysis is a process by which crystallizable substances are separated from non-crystallizable ones, by suspending a solution containing both upon a porous diaphragm having its under surface in contact with water. The crystalloids pass through the diaphragm, while the non-crystalline remain above it, and are termed colloids. Examples of the latter class are gelatin, gum, glue, starch, dextrin, albumen and extractive matters, which are generally the inert and valueless constituents of vegetable drugs. Parchment-paper and bladders are used for the diaphragm; the whole apparatus being termed the dialyzer, while the water into which the crystalloids pass is called the diffusate.
The unofficial preparation known as Dialyzed Iron or Ferrum Dialysatum is a colloidal substance obtained by treating Ferric Chloride in solution with Ammonia, whereby Ferric Hydrate is precipitated and then dissolved by agitation. The mixture being placed on a dialyzer, the crystalloids formed (Ammonium Chloride and Ferric Chloride), together with any free acid present, pass into the diffusate, leaving the neutral colloidal liquid (solution of Ferric Oxychloride) above on the septum.
Maceration is one of the processes of extracting the soluble principles from drugs, and consists in steeping or soaking the comminuted substance in a suitable liquid called the menstruum, generally alcohol, for a period varying from 2 to 14 days, during which it is occasionally agitated. The liquid is then poured off, the residue is expressed, and the mixed liquors are filtered. Several of the official tinctures are prepared by this method, and many others are subjected to maceration first and percolation afterwards.
Expression is the forcible separation of liquids from solids, by subjecting them to pressure. Hand-pressure through straining-cloths may be employed, but mechanical presses are more efficient and are coming into general use. Oils obtained in this manner are called expressed or fixed oils, to distinguish them from the volatile oils obtained by distillation.
Percolation or Displacement is a process of obtaining the soluble constituents of a substance in powder by the descent of a solvent through it. Though an ancient process for the making of lye from wood-ashes (lixiviation), it has only within the last forty years been adopted as an official process in pharmacy, and it is gradually taking the place of maceration as a means of extracting the soluble principles of drugs. The vessel used to hold the powdered drug is called the percolator, of which there are many forms employed by the manufacturers. The liquid used as a solvent is called the menstruum, and when coming from the percolator it is termed the percolate. The U. S. Pharmacopoeia gives the following directions concerning this process:
"The process of percolation, or displacement, directed in this Pharmacopoeia, consists in subjecting a substance, or substances, in powder, contained in a vessel called a percolator, to the solvent action of successive 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 funnel-end should be rather short, and should gradually and regularly become narrower toward the orifice, so that a perforated cork, bearing a short glass tube, may be tightly wedged into it from within until the end of the cork is flush with its outer edge. The glass tube, which must not protrude above the inner surface of the cork, should extend from 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 fit
ting 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 five hundred grammes of powdered material, are preferably the following: Length of body, fourteen inches (36 centimeters); length of neck, two inches (5 centimeters); internal diameter at top, four inches (10 centimeters); internal diameter at beginning of funnel-shaped end, two and one-half inches (6.5 centimeters); internal diameter of the neck, one-half inch (12 millimeters), gradually reduced at the end to two-fifths of an inch (10 millimeters). 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 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 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 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"
Modification of the above Process.
"Authority is given to employ, in the case of Fluid Extracts, where it may be applicable, the process of Repercolation, without change of the original menstruum."
Testing is directed by the Pharmacopoeia in convenient cases, for the purpose of ascertaining the identity and purity of its preparations; and
a List of Reagents used is given at the end of the book, which is divided into three parts,-(1) Articles used in Testing, (2) Test-solutions, (3) Volumetric Solutions. The analysis directed under the title of each preparation is frequently Qualitative, but often Quantitative, and of the latter both the Gravimetric and the Volumetric methods are used. Pharmacopoeial testing and volumetric analysis are necessary to the work of the practical pharmacist, and as the apparatus used is simple and the operations are those in the line of his daily work, he should be familiar therewith. On the other hand the proximate analysis of organic substances for their principles, and the ultimate analysis of the same bodies for their elements, require a high degree of skill and long experience, and should be left to the professional chemist.
The apparatus used in testing consists of graduated flasks and jars, burettes, pipettes, funnels, beakers, test-tubes, capsules, crucibles, reagentbottles, etc. The metric system is directed for all analytical work, and the apparatus employed should be graduated accordingly.
The pharmacopoeial preparations may be presented under various methods of classification, one of the simplest being that which divides them into liquids and solids, the former being subdivided into groups named after their principal bases, viz. :
Aqueous,-Waters, Solutions, Infusions, Decoctions, Syrups, Honeys, Mucilages, Mixtures; the last four containing sweet or viscid substances.
Alcoholic,-Fluid Extracts, Tinctures, Wines, Spirits, Elixirs.
In the following descriptions of the pharmacopoeial groups the composition and dosage of the various preparations are omitted, as they are fully detailed in the section on Materia Medica, under the title in each case of the principal constituent.
Aquæ, Waters,-are aqueous solutions of volatile substances, which may be either solids, liquids, or gases, dissolved either by solution in cold or hot water, by filtration through an absorbent powder, by percolation
through cotton saturated with the substance, or by distillation. The official waters number 15, including the two forms of Aqua itself, as follows, viz.: :
Aqua Ammoniæ Fortior.
Aqua Aurantii Florum.
Of the above-named two are made by simple solution (A. Amygdalæ Amaræ and A. Creasoti), three are made by passing gases through water (A. Ammoniæ, A. Ammoniæ Fortior, and A. Chlori), three are made by distillation (A. Aurantii Florum, A. Destillata and A. Rosa), and the other six are made by percolation through cotton impregnated with the substance. All waters deteriorate when long kept, microscopic plants being propagated in them from spores from the atmosphere. They should be prepared only in such quantities as are needed for use within a reasonable time.
Liquores, Solutions,-comprise all aqueous solutions of non-volatile substances except the syrups, infusions and decoctions, which naturally form distinctive classes. Included among the Liquores is the Solution of Gutta-percha, the solvent of which is Chloroform; all the others being made with water. There are 28 official solutions, as follows,-the first 11 being simple aqueous solutions; the next 16 being chemical aqueous solutions, in which the properties of the dissolved substances are altered by chemical action; and the last-named being a solution in Chloroform.
Liquor Acidi Arsenici.
Liquor Arsenii et Hydrargyri Iodidi.
Liquor Ferri et Quinine Citratis.
Liquor Iodi Compositus.
Liquor Plumbi Subacetatis Dilutus.
Liquor Sodii Arseniatis.
Liquor Ferri Acetatis.
Liquor Ferri Citratis.
Liquor Potassii Citratis.
Liquor Soda Chloratæ.
Syrupi, Syrups,-are concentrated solutions of Sugar in Water or in aqueous liquids. They sometimes contain Acetic Acid, and occasionally Alcohol; and are termed simple, medicated or flavored, according as they are simple solutions of sugar in water alone, or contain soluble medicinal substances, or flavoring ingredients. The Sugar used should be very dry,