IV. Hexagonal or Rhombohedric.-Four axes, three of equal length, in the same plane, and inclined to one another at an angle of 60°. Fourth axis different length, and intersecting the planes of the other three at right angles.

V. Monoclinic or Oblique Prismatic.-Three axes of unequal length; two obliquely inclined to each other, the other axis forming right angles with these two.

VI. Triclinic or Doubly-oblique Prismatic.-Three axes of unequal length, all obliquely inclined to each other.

What is meant by Cleavage? The tendency of crystals to split in one direction more than another.

By what method would you obtain crystals? 1. By fusion and partial cooling (sulphur, camphor, etc.). 2. Sublimation (corrosive sublimate). 3. Deposition from hot, supersaturated solutions on cooling. 4. Deposition during evaporation. 5. Galvanism (deposited while current is passing through solution). 6. Precipitation. 7. By adding a solid substance having a strong affinity for water. (If CaCl, be added to a solution of NaCl, the latter will crystallize out.)

What is meant by Water of Crystallization? In the act of crystallizing, many substances combine with water. This is known as water of crystallization. The amount varies in the same crystal under different circumstances. When crystals lose their water of crystallization, and form a white powder on their surfaces, they are said to effloresce. Crystals that absorb water from the air are said to be hygroscopic. The act is called deliquescence when sufficient water is absorbed to liquefy the substance.

What is meant by Mother liquor? The liquid remaining after the crystals have formed.

What is Dialysis? The separation of crystallizable from non-crystallizable substances by osmosis.

What is a Dialyzer? A vessel with a parchment head, like a drumhead, at one end, into which the substances to be separated are placed in the form of solution. This is floated on distilled water, and by osmosis the crystallizable substance transudes through the membrane into the water below, leaving the non-crystallizable substance behind.

Crystalloids.-Crystallizable substances. Ex., sugar, salt, chemical sub

stances.

etc.

Colloids.-Non-crystallizable substances-glue, gum, starch, dextrine, Diffusate.-The impregnated distilled water.

What is Maceration? Soaking a drug in a solvent until the soluble portions are dissolved.

What is Expression? The process of forcibly separating liquids

from solids.

Name the six mechanical principles employed in constructing presses. 1. Spiral-twist Press. 2. Screw Press. 3. Roller Press. 4. Wedge Press. 5. Lever Press. 6. Hydraulic Press. (For full descriptions of these presses, see Remington's "Pharmacy.")

PERCOLATION.

What is Percolation? Percolation is the process whereby a powder contained in a suitable vessel is deprived of its soluble constituents by the descent of a solvent through it.

By what other name is it called? Displacement.

Give a familiar example. The percolation of water through wood ashes, by which it is exhausted of its potash, etc., the solution being known as lye.

What is the use of this process in Pharmacy? It is used for extracting the virtues of drugs, in the preparation of tinctures, fluid extracts, etc.

Describe a Percolator. A Percolator is a cylindrical vessel with a porous diaphragm below, into which the drug, in the form of a powder, is introduced, and its soluble portions extracted by the descent of a solvent through it.

Describe the rationale of the process. The solvent, which is poured on the top of the powder, in passing downward exercises its solvent power on the successive layers of the powder until saturated, and is impelled downward by the combined force of its own gravity and that of the column of liquid above, minus the capillary force with which the powder tends to retain it.

What is a Menstruum? The solvent is known technically by this

name.

What is a Percolate? The liquid coming from the Percolator, impregnated with the soluble principles of the drug.

Why is Percolation also called the process of Displacement? Because it was first observed that ether, poured on powdered bitter almonds, displaced the fixed oil which it contains without materially mixing with it. Describe the condition in which the soluble principles exist in the powdered drug, and the effect of the solvent upon them. The soluble principles in the powdered drug exist in a hard and dry condition, and are generally contained in cells which are more or less disintegrated in grinding. The solvent takes up first the principle liberated by grinding, and afterward permeates the cells.

Why is it that each succeeding portion of percolate is less highly colored and less active than the one preceding it? Because the first portion of menstruum, in its descent through the powder, has the first opportunity to come in contact with the largest portions of the soluble principles, which are to be found in the finer dust scattered through the powder, and in the thoroughly disintegrated particles, which offer but slight resistance to the passage of the menstruum.

What are the directions of the U. S. P. upon Percolation? The process of percolation, or displacement, directed in this Pharmacopoeia, consists in subjecting a substance, in powder, contained in a vessel called a percolator, to the solvent action of successive proportions 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 funnelend 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 oneeighth to one and one-half inch (3 to 4 centimetres) beyond the outer surface of the cork, and should be provided with a closely-fitting, narrow 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 shape of a percolator should be adapted to the nature of the drug to be operated upon. For drugs which are apt to swell, particularly when a feebly alcoholic or an aqueous menstruum is employed, a conical percolator is preferable. A cylindrical or only slightly tapering percolator may be used for drugs which are not liable to swell, and when the menstruum is strongly alcoholic, or when ether or some other volatile liquid is used for extraction. 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 two-thirds its height. The percolator is best constructed of glass, or stone-ware, but, unless otherwise directed, may be made of any suitable material not affected by the drug or menstruum.

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 its 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 in a basin, the specified quantity of menstruum is poured on, and it is thoroughly stirred with a spatula or other suitable in'strument, 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 to 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.

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 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 of a 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 shall be poured on to displace the absorbed liquid, until the prescribed quantity has been obtained. What is the best Percolator for common use? An ordinary glass funnel.

What is the objection to the glass funnel? It is too broad for use in percolating drugs for fluid extracts when the quantity of drug is large in proportion to the quantity of menstruum.

What is the desirable shape for making this class of preparations? A tall, narrow Percolator.

Why? Because it is desirable that the menstruum should traverse a higher column of powder.

What is gained by this? 1st. Every drop of menstruum is economically applied; 2d, the rate of flow is diminished; 3d, the percolate becomes saturated more rapidly; 4th, the operation is, therefore, more easily controlled.

What general rule may be given for selecting percolators? For making fluid extracts, a tall, straight percolator, should be selected; for

making a strong tincture, the percolator should be slightly bell-shaped and wider; for making weak tinctures, use a funnel.

How would you limit these rules? The character of the drug influences the limit. Those containing a large amount of soluble matter, like kino, cannot be percolated in a tall, narrow funnel, because the percolate would soon become too dense to descend.

What influences the degree of comminution proper for each substance? It depends, Ist, upon the physical structure of the drug; 2d, the ease with which the menstruum dissolves the desired constituents; 3d, the length of time required to exhaust the powder; 4th, the relative proportion of menstruum to drug.

Why does the Pharmacopoeia direct that the drug shall be passed through a coarse sieve after moistening? To render it uniform.

Why should the powder be moistened? Ist, a moist powder, like a moist sponge, greedily absorbs moisture, but a dry powder, like a dry sponge, repels attempts to moisten it; 2d, dry powders have a tendency to swell when moistened, which, owing to the pressure of the particles against each other and the sides of the percolator, prevent menstrua from penetrating them.

State the exceptions to the rule for moistening powders. Powders should not be moistened, Ist, when the addition of the menstruum would produce lumping, owing to the adhesive nature of the drug; 2d, when the moistened powder would offer too little resistance to the passage of the menstrum; 3d, those in which the menstruum is too volatile or too inflammable to render moistening desirable or safe. The cold percolation of sugar in making syrups illustrates the first; the preparation of oleoresins with ether illustrates the second and third.

Of what should the porous diaphragm be composed? Porous cotton, a deeply notched cork, or a perforated plug of cork or wood.

The porous diaphragm should be covered with clean sand, or a disk of scored filter paper, except when absorbent cotton is used. Always moisten the porous diaphragm with a portion of the menstruum before packing the percolator.

How should a percolator be packed? It should be packed in layers, each succeeding layer being packed according to the directions, "moderately' or "firmly," as the case may be, care being taken to use the same degree of pressure with each layer.

How would you test the correctness of the packing? By the descent of the menstruum, which should descend slowly and uniformly. What general rule is given in relation to the degree of pressure to use in packing percolators? Porous, spongy drugs, and menstrua largely aqueous, require moderate packing. If a strongly alcoholic menstruum is directed, pack firmly.

How would you add the menstruum? Cover the top of the powder with a sheet of scored filter paper, place a weight upon it to keep it in place, and add the menstruum in divided portions, care being taken to follow with the succeeding portion before the first one has entirely disappeared, to prevent fissures forming in the powder, and the leaking of the menstruum through the fissures.