stance to be infused should be in a coarse state of division and preferably suspended in the liquid. Decoction represents the solvent action of fluids at their boiling temperature, and is confined to drugs not yielding their active virtues at a lower temperature and where no loss of volatile principles need be feared. Maceration consists in subjecting a mixture of soluble and insoluble matter in a divided state to the solvent action of fluids at ordinary temperature for such length of time as may be necessary to insure complete solution of the principles sought; the process must be conducted in wellclosed vessels, and the contents must be well shaken at least once in twenty-four hours. Frequent agitation is essential if complete extraction of soluble matter is to be insured by maceration, as otherwise a dense layer of a concentrated solution will soon envelop the material and prevent the solvent action of the menstruum from being effective; hence only a small proportion of the soluble constituents will be taken up, as may be readily observed in the slight color and odor of the supernatant liquid if a mixture of asafetida and alcohol, or of opium and water, be set aside for a week without agitation. Digestion differs from maceration only in the higher degree of temperature employed, it being constant during the process, the use of which is confined to substances of very close texture.

9

CHAPTER VIII.

PERCOLATION.

PERCOLATION, or, as it is sometimes called, displacement, is beyond doubt the most important method of solution or extraction in the hands of the pharmacist. The term percolation (from the Latin per and colo, meaning to strain or trickle through) may be defined as a process whereby the soluble constituents of vegetable drugs are extracted by allowing the menstruum to permeate a column of the more or less finely powdered material, the saturated solution being removed as fast as formed, thus continually presenting fresh solvent to the drug. The apparatus in which the process is carried on is known as the percolator, the solution obtained as the percolate, and the residue of insoluble matter as the marc.

Although the idea of solution by percolation did not originate in this country, its present improved and general application is due entirely to American enterprise and ingenuity. The first attempt to extract soluble matter from powdered drugs by allowing a menstruum to exert its solvent action during its passage through a column of the material was made by Count Real in the early part of the nineteenth century, the principle involved being about the same as that utilized by the French in the preparation of their world-renowned coffee. In 1833 M. Boullay, an enterprising French pharmacist, considerably modified the plan of Count Real, and in a series of carefully conducted experiments demonstrated the adaptability of the process of percolation to the extraction of vegetable drugs. So convincing were the results of his investigations that Prof. William Procter and A. Duhamel, prominent American pharmacists, became deeply interested in the work, and in 1839 strongly advocated its adoption as a method of extraction superior to others known at that time. Although the process of percolation was recognized in the United States Pharmacopoeias of 1840 and 1850, it did not meet with the general favor since accorded it until Prof. Israel Grahame, of the Maryland College of Pharmacy, in 1858, suggested some valuable improvements, which led to better results than had yet been obtained. To Prof. Grahame belongs the credit of first advocating the use of powders of uniform degree of fineness as well as the proper moistening of the powdered drug with a sufficient quantity of the menstruum before packing it in the percolator, both of which suggestions are now considered indispensable to successful percolation; at the same time, the use and advantage of a

common funnel for the percolation of many drugs was pointed out. The advantage of properly moistening the powdered drug before packing will be readily understood when it is considered that the material to be operated upon is not a mere mechanical mixture of soluble and insoluble matter, but that the soluble principles to be extracted are intimately held or enclosed by the insoluble cellular tissue, and that penetration of the tissue by the menstruum is necessary to effect solution; the saturation of the powder with the liquid prepares the constituents for ready solution and establishes an affinity between the cellular contents and the fresh menstruum, enabling the latter to permeate the cells by osmotic action. If the menstruum is brought in contact with dry powder, absorption of the former either takes place very slowly or is entirely interfered with, just as dry, hard sponge resists the entrance of water for a long time; the original moist condition of the drug before it was powdered must therefore be re-established before the menstruum can exercise its power of extraction.

The principle underlying the process of percolation may be stated as follows: A solvent or menstruum, poured on the top of a mass of powder consisting in part of soluble matter, supported on a porous diaphragm in a cylindrical or conical vessel, descends from layer to layer by reason of its own gravity and the pressure of the superincumbent liquid, penetrating the particles of powder by reason of surface action, and exercising its solvent power on each successive layer until its power of solution is exhausted, after which it continues its downward flow, as a saturated solution, into the receiving vessel below. This process continues until all soluble constituents have been removed from the powder, the descending menstruum becoming less and less charged with extractive matter. To insure such complete extraction it is absolutely necessary that the material operated upon shall be in a uniform powder and that the capillarity or porosity of the mass be not interfered with in any way, so that the descent of the menstruum may be slow, even, and regular from one horizontal layer to the next.

Different styles of percolators have been proposed at various times, and as drugs vary in their nature and require different treatment to yield different preparations, the pharmacist must be supplied with a variety of percolators, from the conical shape of the ordinary funnel to the nearly cylindrical. The choice of percolator depends largely upon the character of the percolate to be obtained, and also upon the nature of the drug; for instance, if a very strong solution is to be prepared with a minimum quantity of menstruum, a narrow cylindrical percolator is preferable, so that the solvent is made to pass through a long column of the drug and thus become thoroughly saturated; a cylindrical, or only slightly tapering, percolator is also indicated when the menstruum is strongly alcoholic, or when ether or some other volatile liquid is used for extraction. The advantage of using a long, narrow percolator with the view of

FIG. 99.

a

economizing menstruum when concentrated vegetable solutions are to be made, may be easily demonstrated by means of two percolators having the same cubical capacity, but of such difference in shape that the diameter of the one shall be exactly one-half the diameter of the other, and that the narrower percolator shall be four times as long as the other, as shown in Fig. 99, A and B. Suppose a given quantity of drug is packed into A and fills the same up to the line e, and then a like quantity of drug be packed into B; if we assume the mass in 4 to be divided into two equal sections, a and b, by means of the plane de, it is fair to assume that the same quantity of material in the respective sections a and b when packed in B, instead of occupying adjoining spaces as in 1, would lie one above the other. If it requires 10 liters of menstruum to exhaust completely the drug in 4, it may be assumed that the sections a and b required equal amounts, or 5 liters each. If 5 liters of menstruum be now poured upon the column of drug in B, this quantity of menstruum will prove sufficient to exhaust completely the upper section, as the same quantity of solvent proved adequate for the complete exhaustion of an identical quantity of drug in 4; but the solvent powers of the menstruum will not have been entirely spent, and hence as it passes downward through the lower section b it will continue to extract soluble matter until fully saturated, and then flow off into the receiving vessel. All the soluble matter in a and a portion of that in taken up by the 5 liters of menstruum used, another portion of menstruum is poured on the top of the column, and as there is no soluble matter left in a, it will be necessary only to extract the soluble matter still remaining in 6, for which purpose 2 or 3 liters of menstruum will suffice. Thus in connection with percolator B, 7 or 8 liters of menstruum are found sufficient to exhaust completely a quantity of drug which in percolator 4 was found to require 10 liters of menstruum, showing a saving of

a

having been

d

C

B

about 20 or 30 per cent. If, on the other hand, the quantity of

drug to be extracted is small in proportion to the menstruum, as in the majority of official tinctures, a wider percolator, of the shape and style shown in Fig. 100, may be used, in which the liquid will traverse the column of drug more rapidly and yet be able to exhaust it thoroughly, owing to the larger amount of menstruum at the disposal of the operator. When drugs such as gentian, senega, rhubarb, orange-peel, and others, which have a tendency to swell considerably, particularly with aqueous or feebly alcoholic menstrua, are to be percolated, a common funnel will often be found advantageous on account of the ample allowance for lateral

expansion of the moist drug. The size of the percolator selected should be in proportion to the quantity of drug to be extracted; when properly packed in the percolator the drug should not occupy more than about three-fourths of its height.

The covered tin percolator (Fig. 101) consists of a cylinder varying in size and tapering somewhat toward the funnel-shaped end, provided with two perforated diaphragms fitting loosely into the cylinder, the lower of which should be more finely perforated than the upper. The stopcock in the neck of the funnel serves the