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Related post: 28 MANUAL OF PHARMACOLOGY FIG. i. Method of percola- tion (Thornton). portions of the powder will be entirely exhausted whilst others are still scarcely affected. The lirinnos of the packing is also of great importance; if not firm enough, the men- struum will run through too rapidly and the percolate will consequently be weak. If too lirm it can not run at all; and if any swelling occurs the percolator will be broken. Drugs in co;ir>e powder should be packed more firmly than fine powders. An alcoholic menstruum requires firmer packing than a watery one. The {Kicking being completed, the menstruum is Buy Isosorbide poured on until it stands an inch or two above the drug; the percolator is then covered and set aside for maceration for a specified time, the tube being raised so that no liquid flows out. When the time of maceration is completed, the tube is lowered and fixed at such a level that the outflow occurs at the rate of 2 to 15 drops per minute. New menstruum is poured on in the measure that the old flows out. Care should be taken always to maintain the layer of liquid above the powder; else cracks may appear in the latter, necessitating re- packing. The process is continued, in the case of tinctures, until a certain volume of percolate is obtained. The quality of the percolate will, of course, depend upon the care and skill of the operator, and the product is apt to vary. Macera- tion would, therefore, be a better process for tinctures. This difficulty is avoided in the case of extracts, for here the percolation is continued "until the drug is ex- hausted;" i.e., until the active ingredients have become completely dissolved out. This is recognized by testing the last portions of the percolate in the appropriate man- ner, such as Mayer's reagent for alkaloids, water for resins, etc. It may here be remarked that a drug is usually more rapidly exhausted Cheap Isosorbide of its active ingredients than of its coloring-matter, so that the last portions of percolate may be colored and yet devoid of activity. The choice of a menstruum must be determined by the nature of the constituents. The object is, to extract all the active ingredients and the minimum of inactive. Alkaloids and resins require strong alcohol; gums, weak alcohol; licorice, alkaline alcohol; san- guinaria and ergot, acidified alcohol; gentian and quassia, water plus alcohol enough to keep. Pharmaceutic Solvents. The most useful are the following: Water or Glycerin. Dissolve salts (including those of alkaloids), sugar, gums, tannin, acids, and alkalies, etc. Dilute Acetic Acid. Especially for alkaloids. Alcohol. Dissolves alkaloidal salts, neutral principles, resins, volatile oils. Precipitates gums and most inorganic salts. Ether, Chloroform, Acetone. Dissolve free alkaloids, neutral principles, resins, volatile and fixed oils, and fats. Petroleum Benzin. Solvent properties as the preceding, except resins. - 1 romatic Spirits of A mmonia. Dissolves resins and organic acids. In the case of very volatile menstrua, such as ether, chloroform, or petroleum ether, some means must be employed to collect and return the evaporated solvent. One of the best apparatus of this kind is the familiar Soxhlet extractor. Expression. The process of separating a liquid from a solid by pressure. Its principal employment in pharmacy is for the recovery of tinctures from the "marc," i.e., the liquid retained by the drug residue after maceration and percolation. It is also a process of separating fixed oils. The drug is put in a coarse strong cloth and subjected to pressure in a press. These are of various patterns; screw, lever, hydraulic, or centrifugal. The pressure must be applied gradually to prevent the bursting of the cloth. Small quantities can often be pressed sufficiently by putting them into a cloth and tightly twisting the end. Straining or Colation. The process of separating solid coarse particles from a liquid by pouring it through a cloth or strainer. PHARMACEUTIC METHODS 2Q Filtration. The process of separating solid particles (fine or coarse) from a liquid by pouring it through a finely porous material, Generic Isosorbide such as filter-paper. The usual material for nitration is pure unsized paper, "filter-paper," which is made of various grades white and gray and of varying texture and thickness according to the purpose for which it is to be used. There are two principal methods of folding a filter plain and plaited. These two filters have different uses. The plaited filter offers a much larger surface for filtration and is therefore more rapid; it is the form usually employed in pharmacy. The plain filter, on the other hand, facilitates washing and removal of the precipitate, and is of more frequent use in chemistry. Other materials are sometimes employed instead of paper. A very useful filter for large quantities of liquid is made from felt. A plug of glass-wool or asbestos placed in the tube of the funnel is especially useful for strong acids or alkalies. A cell of porous clay is also employed, as in the various forms of the Chamberland filter. With this a vacuum is indispensable. Dialysis. This is sometimes used to separate crystalloids (alkaloids, salts, etc.) from colloids (extractives). Decolorization. It is often desirable to remove the coloring-matter from a solution. This may sometimes be accomplished by choosing appropriate solvents. More often, however, the solution is filtered through recently calcined animal charcoal. This very often retains some of the active constituents as well as the coloring-matter. Clarification. The process of rendering turbid mixtures clear and transparent, by
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