an air-pump (G), which is connected with it by means of the tube (F). The stop-cock (H) is next closed and (M) opened, connecting with the tube (E), the end of which dips into the liquid to be employed as menstruum, and thereby a sufficient quantity of it is allowed to be drawn into the displacer to cover the drug. The stopcock (M) is then closed and the materials allowed to macerate for several days. To start the percolation the receiver (C) is exhausted of air and the tap (I) having been opened the saturated fluid will begin to drop, and continue to do so so long as the force of the vacuum in the receiver is equal or greater than that in the upper vessel. When it begins to stop, air is admitted above the drug, which is drawn through the material, carrying with it much of the remaining liquid. To finish the operation air is forced into the percolator by means of the pump.'

FIG. 313.

α

D

A

HOT EXTRACTION.-For the exhaustion of a drug by means of a hot menstruum various forms of apparatus have been offered; very few, however, are adapted for the use of the apothecary for extracting from one to five pounds of drug. One of the most convenient forms for pharmaceutical operations is Lewin's Extraction Apparatus (Fig. 313). This is adapted for (1) continuous extraction with hot menstrua, (2) continuous extraction with b cooled menstrua, (3) recovery of the menstrua from the finished extract by direct distillation. The apparatus is composed of three easily separable principal parts: C, the tinned copper still, B, the copper percolator, which is provided with three movable sieve bottoms for the reception of the substance to be extracted. A is the condenser.

B

O O

୯

For the Continuous Extraction with Hot Solvents, the vapors pass from the still, C, in the tube 1, and enter through the tri-faucet I, when in position a, through tube 4, into the percolator, B, penetrate the substance to be extracted, and condense. The percolate passes into the receiver and from this flows through the tri-faucet III, in its position a, through the tube 7, again into the still, to repeat this course as long as may be necessary or desirable. To prevent pressure in the apparatus, the tube 2 is removed during this operation, and the tri-faucet II is placed in position a. This admits the vapor into the cooling worm, A, which thus forms a safety valve.

Lewin's Extraction Apparatus.

For the Continuous Extraction with Cooled Solvents, the vapors pass from the still, C, into the tube 1, and enter through the tri-faucet I, in its position b, through tube 2, into the cooling worm, A, from this as liquid through the tri-faucet II, in its position

a, into the percolator, and so through the substance to be extracted into the still as before.

For the Recovery of the Solvent from the Extract by Direct Distillation, the vapors pass from the still, C, through tube 1, through the tri-faucet I, in its position b, through tube 2, into the cooler, A, through the tri-faucet II, in its position b, into the exit tube 3, which latter may be lengthened at pleasure.

Portions of the percolate may be removed from the receiver at pleasure through the tri-faucet III, in its position c, by the tubes 2 and 3. All of the tubes are connected or disconnected by good screw-joints.

Fig. 314 illustrates the extraction apparatus of C. O. Currier, which recommends itself for simplicity and cheapness.

FIG. 314.

Currier's

R

M

It consists of a glass flask, O; glass percolator, K; and a condenser, R. The condenser is the only part that will have to be made; the other parts of the apparatus are to be found in almost every laboratory. The condenser is a modification of the Liebig condenser, consisting of a number of tubes instead of one, thereby increasing the condensing surface and distributing the condensed liquid evenly over the surface of the drug. The condenser is made in the following manner: A tube of tinned copper is made one inch less in diameter than the top of the percolator to be used, and about two or three times as long as its diameter. A cap of tinned copper (tinned side out) is fitted to each end of the tube. The tube is traversed by tin tubes (made by cutting off blocktin pipe to the proper length) that project three-fourths of an inch below the lower cap, and are cut off obliquely to facilitate the dropping of the condensed liquid. One of the tubes, A, is in the center, and passes through the upper cap about six inches, to which a bent safety tube may be attached to prevent undue pressure to the apparatus. The other tubes, G, H, C, D, are closed at the top and pass into the condensing tube to within one-half inch of the top, and are arranged in a circle around the central one. Their number can be increased or diminished according to the size of the apparatus, four or five being sufficient for a pint percolator. Holes for these tubes should be made through the lower cap just the size of the tubes, and the tubes soldered to the cap 2, on the inside before the cap is soldered to the condensing tube. A small brass tube, F, is inserted in the condenser near the bottom and one near the top, B, for the entrance of cold water and exit of warm water. A cork is chosen that will fit tightly into the top of the percolator, and a circular piece cut out of it, just the size of the condenser, R, and is put upon the lower part of it at E. The cork can be kept in place and prevented from slipping up the tube when pressing into the percolator by soldering a collar of tin to the condenser at a distance from the bottom equal to the thickness of the cork.

The apparatus is used in the following manner: A cork, N, with longitudinal channels cut in its surface, is inserted in the neck of the percolator, K; through the center of the cork, a glass-tube, L, is passed to within two inches of the top of the percolator. The tube should be bent over at the top, to prevent its being clogged up by the drug while packing it into the percolator. A little cotton is placed in the percolator and pressed down upon the cork, and the drug packed in the usual manner. The percolator is then fitted into the neck of the flask, O, by means of a perforated cork, M, the liquid to be used as a menstruum having been previously put in the flask. The condenser is then connected firmly with the top of the percolator. The joints are luted with ground flax-seed mixed

Extraction Apparatus.

into a stiff paste with water. The tube F is connected with a supply of cold water by means of a rubber pipe, and the tube B with a sink, or waste-pipe. The apparatus thus put together is placed in a water-bath and the heat applied. The flask should be immersed in the water to the point marked S on the neck. After the drug is exhausted the percolator is removed from the flask and the flask is connected by means of a bent tube with a Liebig's condenser, and the liquid recovered.

For apparatus adapted to the extraction of smaller amounts of substances, see Oleoresins, page 290.

CHAPTER XXV.

EXPRESSION.

Expression is forcible straining. The separation of fluid from solid matter is effected in small operations by hand, the straining cloth being used (Fig. 256). On the larger scale, as in the removal of the last portions of fluid from drug residues, it is accomplished by means of presses or the centrifugal machine. Expression is a necessary part of the process of Maceration; it is also required in the operations of Percolation, for the removal of menstruum adhering to the dregs or "marc." In some instances, the mass is thrown directly into the press or centrifugal machine; in others, it is first enveloped in a strainer of press cloth, before being subjected to pressure.

For the purpose of enclosing the material which is to be subjected to pressure, we employ the press-cloth or bag; this must be made of a material sufficiently strong to withstand great pressure without rupture. For this purpose strong canvas may be used, or, better, the so-called press-cloth, which is specially made for this purpose. In conducting the process of expression, pressure should be applied very slowly, otherwise, should the substance contain much fluid, the cloth will be ruptured. After the greater part of the liquid has been pressed out and the pulp has become firm, the pressure may be gradually increased to the full power of the press. The compression should be carried on in stages, the press being allowed to rest a few moments after each increase of pressure, thus allowing a new portion of the fluid an opportunity to drain off, and at the same time affording the particles of the mass an opportunity to assume their new positions in closer contact. Each subsequent increase of pressure will require a comparatively smaller effort.

SCREW PRESSES.-Fig. 315 illustrates the more common form, which consists of a vertical screw operated by a lever, the lower end of this screw fitting into a cavity in the top of the plunger, which is free to move about in the limited space of the cylinder. The body of the press consists of an outer metallic casing, which serves to receive the fluid when forced through the perforated sides of the inner cylinder. All the parts of the press, which come in contact with the drug or fluid, should be well tinned, to prevent rusting, also to avoid discoloration or injury to the product should it contain tannin-like principles or acids. or acids. The drug to be expressed should be first carefully enveloped in a moistened presscloth (if straining has not been performed), care being taken to fold over the corners, so as to form a square, compact pack. For

this purpose, the cloth should be sufficiently large, so that there may be no danger of the drug being forced out. The pack, or

the loose drug, if it should require no press-cloth, should be placed

uniformly in the cylinder, so that it may receive equal pressure on all sides.

Fig. 316 illustrates the Differential-arm Screw Press, in which the arm is moved back and forward in a half-circle, whereby the screw is forced downward. This is the most powerful hand screw press made.

Fig. 317 illustrates an elegant screw press designed by Prof. Witt, which is specially adapted for expressing strongly acid or alkaline liquids from masses. It recommends itself for all purposes, since the press-block and all the parts with which the

fluid comes in contact are made of the strongest porcelain.