Pills are spherical, more or less soluble masses of medicinal substances rendered cohesive, plastic, and finn in consistence by the addition of some substance (usually inert) termed an excipient.

The kind of excipient employed varies with the nature of the medicinal substance. As a general rule, such substances are chosen as give to the mass, with the smallest proportion, the greatest plasticity, and also best preserve the spherical shape of the pills. The excipient must also, unless the contrary be directed for especial purposes, be indifferent in character, to avoid change in the medicinal agents.

Soluble substances are rendered adhesive by the action of solvents, and require, according to their solubilities, the addition of some liquid such as Water, Alcohol, Glycerin, etc. Others require the addition of adhesive substances, such as Syrup, Mucilage, Glucose, Glycerite of Starch or Tragacanth, etc.

Drugs adapted for dispensing in the form of pills may be divided as follows:

(1) The official Masses, Extracts, and Scaled Salts.

Masses and extracts, being of pilular consistence, require no addition except when hard or dry; Water should then be incorporated to restore them to their original form. Powdered extracts are best made into a mass with Water.

(2) Vegetable Powders in which the dose does not exceed five grains.

With these adhesive excipients are indicated, such as Syrup, Mucilage, Glycerite of Tragacanth, and Glucose. The last mentioned answers the requirements better than most other substances. Confection of Rose and Extracts of Gentian, Glycyrrhiza, and Taraxacum are also used when their color is not objectionable.

(3) Salts not too deliquescent, and Alkaloids.

Excipients for these must combine adhesive and absorbent qualities. They are first triturated with a dry powder - e. g. Althaea, Glycyrrhiza, or Milk Sugar - and then mixed with the adhesive substance - viz. Glucose or Glycerite of Starch or Tragacanth.

No excipient must be used that will give to the mass a color different from that of the medicinal ingredients (the base).

(4) Volatile Oils and Oleoresins.

The quantity of these when dispensed in pills being comparatively large, it is necessary to add some light absorbent substance, such as Magnesia or Starch, to which is added the adhesive material. The practice of adding wax or resin to oils is not to be recommended except as a last resort, since they tend to render the pill insoluble.

(5) Resins and Gum Resins.

These form an adhesive mass by the addition of a little Alcohol, with which more bulky excipients, such as Soap, may be incorporated to preserve the shape of the pill.

(6) Salts of the Cinchona Alkaloids, Quinine and Cinchonidine Sulphates, etc.

These are often prescribed in pill form in large doses, and it is therefore desirable to reduce their bulk. For this purpose dilute Sulphuric Acid or Tartaric Acid is added in small quantity, which acts as a solvent upon the salt, thereby converting it into a mass.

This mass is incorporated with a little Glycerite of Starch, other-wise it soon loses its plasticity; it must therefore be rolled into pills as soon as formed.

(7) Substances easily decomposed by organic matter.

Potassium Permanganate and Silver Nitrate are quickly "re-duced" when incorporated with the excipients usually employed.

These should be mixed with an inorganic diluent not affected by them, such as Kaolin, Pipe Clay, or Fullers' Earth, and made into a mass with Water, Petrolatum, etc.

The following Pills are official:

1 Coated with ethereal solution of Balsam Tolu. 2 Phosphorus dissolved in Chloroform.

In order to disguise the bitter or otherwise disagreeable taste of pills, they are usually coated with sugar or gelatin. These coated pills are often objectionable on account of the coating, or the pill itself, becoming quite insoluble. When a coated pill is desired, it should be freshly made and enclosed in a gelatin capsule of the smallest size. Pills may also be coated extemporaneously by rolling them on a piece of filter-paper saturated with Mucilage of Acacia, and then in powdered Milk Sugar.

Keratin-coated pills are designed for solution in the duodenum, the pills being dipped in a solution of Keratin prepared from horn shavings treated with pepsin and hydrochloric acid. Keratin is insoluble in the acid gastric juice.

Concentric pills are made up of concentric layers of different ingredients, intended to dissolve and become active at various stages in their passage through the intestinal tract.