an extra number of tablets (4 or 5) made out of the plain diluent, added to the number first obtained, before the whole is thoroughly mixed in a mortar; this extra material is necessary because the first tablets, when worked up again in the mortar, generally form a more compact mass, and hence would prove insufficient for refilling the required number of perforations.

Tablet triturates are, beyond doubt, far more readily disintegrated than compressed tablets, but the latter form has a larger range of applicability, owing to the many variations in quantity and composition; tablet triturates above 5 grains in weight become inconveniently bulky, and, being flat on both sides, are less readily swallowed than even larger compressed tablets of lenticular shape.

Hard-rubber moulds require considerable care in cleaning and in storing them when not in use, in order to preserve the original perfect shape. They should never be exposed to heat, either by using hot water for washing or dry heat for drying them, as the moulds are thereby warped and the accurate adjustment of the pegs and perforations is destroyed; when thus warped, the moulds can only be used with great difficulty, and soon become worthless. A narrow, stiff paint-brush will be found very serviceable in cleaning the moulds, and water at the ordinary temperature should be used for washing the plates; sometimes alcohol, or even acids, may be necessary to remove material tenaciously adhering to the moulds, but never should a sharp instrument be used in the perforations or on the pegs, as the smooth surfaces are likely to be scratched thereby. After the plates have been carefully cleansed and rinsed with cold water they should be dried with a soft towel, the water remaining between the pegs being readily shaken out; when dry, the perforated plate should be placed in proper position on the peg-plate, and the whole laid aside on a level, solid surface, away from heat.

Hypodermic Tablets are simply tablet triturates intended for the convenient preparation of solutions for subcutaneous injection. Since they contain definite quantities of the active agents, they are admirably adapted for physicians' use at the bedside, and are very extensively employed. As a rule, pure sugar of milk or pure cane-sugar is used as the vehicle, although sodium sulphate has also been employed by

some manufacturers.

Tablet Saturates differ from tablet triturates only in the manner of introducing the medicinal agents. They are made by first preparing plain sugar of milk tablets, in the moulds already described, and having placed the tablets, when dry, on a glass plate, the desired quantity of tincture, fluid extract, or solution is dropped upon each tablet individually from a pipette. A glass cover is then placed over the tablets and the fluid allowed to saturate them uniformly, after which they are dried in a current of warm air.

CHAPTER XXXI.

POWDERS.

In addition to what has already been said about pulverization, in the chapter on Mechanical Subdivision of Drugs, there remains yet to be considered the administration of medicines in powder form, which, presenting certain advantages, is still largely employed by physicians. The powder form is a most convenient method of giving medicines in the case of very small children and persons who are unable to swallow pills, as well as where the fluid form is unavailable for any reason. It is true, many substances are not suited for administration in powder form, particularly bulky vegetable powders, deliquescent salts, and such as contain large quantities of water of crystallization, as sodium phosphate or sulphate, etc.; but while the fluid form of medicine is probably to be preferred in the majority of cases, the bitter or nauseous taste of some substances becomes more marked in solution than in the dry state. Among the substances best adapted for dispensing in powder form are insoluble chemicals,

FIG. 241.

such as calomel, bismuth salts, sulphurated antimony, some salts of the alkaloids, and vegetable drugs given in small doses, such as ipecac, opium, and catechu. Physicians frequently direct their patients to dissolve or mix the powder in water, and, in such cases, the powder form is preferred on account of convenience or for reasons of economy.

Powders, as a rule, are composed of two or more substances; to insure an intimate and uniform mixture they must be triturated in a mortar, preferably made of porcelain, of the shape shown in Fig. 241, this style presenting a sufficiently broad surface at the base, whilst its curved sides prevent the ejection of material during trituration. It is assumed that, in the majority of cases, the individual ingredients are already in the state of very fine powder, and, therefore, only require thorough mixing, which is best accomplished by trituration with light pressure only, so as to avoid caking and sticking to the sides of the mortar; the contents of the vessel should also occasionally be scraped down from the pestle and sides of the mortar, if necessary, as this aids more perfect admixture. Whenever substances which are themselves in

a coarsely powdered or granular condition, are ordered in a powdered mixture, they must be reduced to a very fine powder by themselves, no attempt being made to reduce them in the mixture.

A few general rules will serve for guidance in the preparation of mixed powders. Whenever sugar is one of the ingredients it should be of the kind known as bolted or lozenge sugar. When small quantities of potent or other substances are to be dispensed in powders, they should first be well triturated with a portion of the diluent, and, finally, incorporated with the remainder of the more bulky powders; or, if no diluent has been ordered, they should be triturated with a small quantity of sugar of milk, to insure their more uniform distribution in the mixture. The proper plan is to place about 5 grains of sugar of milk in the mortar, add the active ingredient, and then triturate thoroughly, as, by this means, more accurate subdivision is effected, and none of the active material is likely to adhere to the sides of the mortar. Soft extracts and essential oils must be treated in the same manner.

Whenever physicians prescribe quantities which cannot be weighed conveniently, such as, o, 24, or of a grain, and metric weights less than 10 milligrammes, the plan of preparing a dilution of the substance with sugar of milk, by trituration, in such proportions that a weighable amount of the mixture shall represent the desired quantity of active ingredient, as already indicated on page 309, should invariably be followed, as by this method accuracy of division is best obtained.

Certain substances of a crystalline structure-notably also those of a resinous character-have a tendency to become electrical by friction, particularly if pressure be employed; such bodies are said to be idioelectric, and must be triturated lightly, or, if pressure is necessary to reduce them to fine powder, they must be sprinkled with a little alcohol, whereby the trouble is obviated, or the powder, which adheres firmly to the mortar and pestle, and is apt to fly off in all directions if scraped with a spatula, must be set aside for awhile until the electric condition has disappeared. To this class belong common pine resin, and the resins of guaiacum, jalap, and scammony, also quinine alkaloid, acetanilid, salol, phenacetin, and others. The removal of these in fine powder form from the mortar is attended with more or less difficulty, unless previously slightly dampened.

When substances which differ materially in specific gravity are to be mixed in powder form-as, for instance, bismuth subnitrate with magnesia, sodium bicarbonate with charcoal, or zinc oxide with lycopodium-the best plan is to place the heavy substance in the mortar and incorporate the lighter body gradually by adding small portions at a time. Calcined magnesia and charcoal are also more readily mixed if the charcoal be gradually added to the magnesia with very light trituration; only in this manner can a powder of uniform appearance be obtained. Whenever large quantities of these pow

ders are to be mixed, perfect blending may be achieved by shaking them together in a bottle for some time, and then passing the mixture repeatedly through a bolting-cloth sieve.

Since some substances when triturated together cause chemical decomposition, attended in a few cases also with explosion, considerable care must be observed in mixing them; the offending ingredient should be reduced to fine powder by itself, and then cautiously mixed on paper with the other powders. Such conditions arise when potassium chlorate or permanganate is to be mixed with organic substances, as sugar, starch, tannin, gum-arabic, and also sulphur and sulphides, or when lead acetate and zinc sulphate or borax and alum are triturated together.

Powders, whether simple or compound, intended for external application, by dusting or insufflation, must be passed through a fine bolting-cloth sieve, and should not then be triturated again before they are dispensed.

In the majority of cases medicines prescribed in powder form are dispensed in divided doses; although absolutely accurate division can only be obtained by weighing, this plan is rarely followed, since practice will soon enable one to omit this tedious method. Usually the operator divides the mixed powder by the eye, either directly on the powder papers or by shaping the powder into a rectangle on a graduated tile, and dividing this into the requisite number of parts; an experienced dispenser is able to make quite accurate divisions from the mortar direct to the paper.

To facilitate the division of doses at the dispensing counter a very neat powder-divider was designed, some years ago, by J. C. Michael, a former pharmacist; it is shown in Fig. 242. The apparatus con

sists of a cup with base attached, a set of three dividers, with 8, 10, and 12 wings respectively (one of which is shown in the illustration), and a cap with sliding door. It is operated as follows: The thoroughly mixed powder is placed in the metallic cup, B, and,

after shaking down so as to obtain a level surface, the metallic divider, D, is slipped over the rod, A, and allowed to work its way slowly down to the bottom of the cup; by slight manipulation, such as gently rotating the divider, the powder will be divided into as many equal parts as wings are attached to the divider. The cap, E, which fits snugly over the projecting wings of the dividers, and is held in position by means of a central pin, is next attached, and, the cup having been inverted, the rod, A, is removed by turning the base, C, held by a bayonet-joint, and withdrawing the rod from the centre of the divider. The powder will now be found transferred to the cap, but divided, as before, since the wings of the divider extend beyond the rim of the cup to the full depth of the cap; by bringing the apparatus over the centre of the paper one portion can be deposited at a time by pulling back the slide, F, and allowing the powder to fall upon the paper. It is, of course, important, when placing the cap on the cup, so to adjust it that the edges of the opening be on a line with two of the wings, which is best done with the slide open. By carrying the apparatus from paper to paper and rotating the divider, each succeeding section can be emptied, and thus rapid division of the mixture be effected. The whole apparatus is nickel-plated, which protects it against rust. Very accurate work can be done with this apparatus, and the necessary experience for rapid manipulation is easily acquired.

Another convenient device for those who do not wish to entrust division of powders to the eye is the Diamond Powder-divider. This consists of a nickel-plated, shallow, metal trough, closed at one end and graduated on both sides; the powder having been introduced, a hard-rubber plug is inserted at the open end and pushed up to the graduation indicating the number of divisions to be made. After levelling the surface of the powder by means of an accompanying flat bar, with handle attached and exactly fitting into the trough, the rubber plug is removed and a quantity of the material, equivalent to one dose, as indicated by the divisions of the graduated sides, is transferred to paper by the aid of a spatula of the same width as the interior of the trough. The dimensions of the trough are 9 inches in length, 1 inch in width, and 3 of an inch in depth.

For enclosing the divided doses of powder, either well calendered or parchment paper may be used; the latter is now preferred by many pharmacists, as it offers a protection against the moisture of the air. Even those who use glazed white paper will find either parchment or waxed paper necessary for volatile or hygroscopic substances. Powder papers should be folded uniformly, hence it will be found advantageous to keep in stock a supply of the various sizes already creased. This is readily done by folding the paper over a piece of stiff metal of suitable size, with rounded edges to prevent cutting, in such a manner that a narrow margin, about inch wide, is made on one of the long sides; the straight edge having been brought up against the crease of the margin, both ends are