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 fitting 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, onehalf 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 Preparation of the Percolator and Material for Percolation. 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, while 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 the 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.

The Manipulation of Percolation.-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 pharmacopœial quantities, shall not exceed the limit of ten to thirty drops in a minute. A layer of menstruum must constantly be main

tained 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 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. What is repercolation?

It is the process of percolating successive portions of powdered drug in such a manner as to make a fluid extract without evaporation. For example: Divide thirty-two parts of powdered drug into four portions of eight parts each. No. 1 is moistened, packed, macerated, and percolated until exhausted. Reserve the first six parts, and use the remainder to macerate No. 2, which, percolate and reserve eight parts; repeat the process with No. 3 and No. 4, reserving eight parts of percolate from each. Mix the reserved portions, thereby making thirty parts total. The weaker percolate of the fourth portion is reserved for subsequent operations, when from each eight parts of drugs eight parts of percolate are obtained. (Dr. Squibb's process.)

It has been proven that the first twelve ounces of percolate contains from seventy to seventy-eight per cent. of the total extract obtainable from sixteen Troy ounces of drug. This process is sometimes called fractional percolation.

Why is percolation sometimes called displacement?

Because of the theory that successive portions of solvent displace the portions which preceded them. This is practically only partially the case.

What kinds of materials require fine comminution for percolation, and what require coarse?

Woody materials may be finely powdered; fleshy and easily permeable tissues may be coarsely comminuted.

Why is the powder moistened and afterwards sieved?

As stated under maceration, the cells are softened and expanded. Sifting, after maceration, is necessary to break up the agglutinated lumps and render the powder uniform in character. Can any powder be percolated successfully without previously macerating?

Substances containing volatile oil and resin, such as ginger (and when the menstruum is light and volatile, as alcohol or ether), are better percolated by first packing the dry powder in a percolator.

What is circulatory displacement?

The substance to be extracted or dissolved is tied in a bag and suspended in the upper part of the menstruum. The heavy extractive matter falls through the liquid to the bottom of the vessel, the lighter menstruum circulating displaces the heavier liquid until the material is exhausted.

From common utensils what may be extemporized as a percolator?

An ordinary funnel or a conical chimney of a lamp makes a very good percolator for small quantities.

Why should the general shape of a percolator be tall and narrow?

Because it is desirable that the menstruum should traverse a long column of powder.

Vaporization.

What pharmaceutical operations does vaporization include? It includes the three operations-evaporation, distillation and sublimation.

Which of these are commonly used in the treatment of organic material?

Evaporation and distillation. (Sublimation is largely employed in the treatment of inorganic material.)

What apparatus is required for conducting the first named operation?

Evaporating dishes.

Mention some of the principles involved in these processes.

The quantity of vapor that will form in a confined space is constant for the temperature, and when an atmosphere is saturated, vaporization ceases unless some circumstances concur to remove a portion of the vapor by condensation.

Rapidity of evaporation is influenced by the state of saturation of the air in contact, being inversely as the quantity of vapor existing in it, when the liquid does not boil.

The boiling points of homogeneous liquids are uniform, provided the pressure is the same; but, if solid matter is in solution, the temperature rises until saturation is attained. Liquids in vaporizing render a large amount of heat latent, which, on condensation, becomes again sensible.

The boiling point rises owing to pressure when a liquid is heated in a tight vessel.

The boiling point is affected by the cohesion and depth of the liquid, and by the nature of the material and surface of the vessel.

Evaporation below boiling is in ratio to the extent of surface exposed to the air.

Evaporation by boiling is in ratio to the extent of surface of the vessel exposed to heat.

What are the various modes of evaporation?

Spontaneous evaporation in vacuo; over lime or sulphuric acid, at the common temperature (processes chiefly used in analytical operations.)

Spontaneous evaporation in the open air, in shallow vessels or on a revolving cylinder.

Evaporation by heat, artificially applied, varying from 100° to 212° F.

Evaporation in vacuo with steam heat, so as to boil at a low temperature.