In the liquid form medicines may be given internally, or applied to the surface. In the former case, if taken in any considerable quantity, they receive the name of potion (polio), or draught (hauslus); the former being sometimes applied to a quantity of liquid which may be taken in divided doses, the latter exclusively to a single dose. Applied to the surface, they receive the name of lotion (lotio) when thin and watery, and of Liniment (linimentum) when of a soft oleaginous consistence, fitted for application by gentle friction with the hand. One of our late officinal liniments (Linimentum Saponis Camphoratum, U. S. 1850) was of the consistence of a soft solid when cold, but became quite liquid at the temperature of the body. Some medicines are essentially liquid, as castor oil, glycerin, etc.; others are brought to the liquid form by admixture and suspension, or by solution. The following are forms of officinal liquid preparations.

Mixtures. Misturae

1. Mixtures (misturae), in the sense of the term as employed in the U. S. Pharmacopoeia, are preparations in which a medicine, insoluble in water, is suspended in that fluid, pure or variously medicated, by means of viscid soluble substances, as gum arabic, sugar, and the yolk of eggs.* The term julep embraces both these preparations and others in which the mixed substances may be dissolved. The form of mixture is one of the most common and convenient for the administration of Insoluble medicines. As a general rule, the medicine is so proportioned in the mixture as to render the dose a tablespoonful (f ss) for an adult.

* In the U. S. Pharmacopoeia of 18G0, one preparation was admitted, in derogation of this rule, among the Mixtures, that, namely, of Mixtura Potassae Citratis, which is strictly, as it was called in the Pharmacopoeia of 18540, a solution of citrate of potassa. (Note to the third edition).

Solutions. Liquores

2. Solutions (liquores) are preparations in which the medicine, or its retire principle, is dissolved in water or other menstruum. The officinal Solutions (Liquores, U. S.), now first adopted as a pharmaceutical class in the U. S. Pharmacopoeia, are exclusively aqueous solutions, with one. single exception, that of Liquor Gutta-perchae, in which chloroform is the menstruum. In relation to medicines which are wholly soluble, the process is extremely simple; and the only rule requiring attention is not to mix, in the same solution, substances which will undergo mutual decomposition, so as to form an insoluble precipitate. In administering in solution substances, the absorption of which is desirable, it is important that, if irritant in their character, they should be so far diluted as to produce as little irritation as may be of the alimentary canal. Medicines generally find a readier entrance into the system when largely diluted than when concentrated. Under the head of solutions may be considered various officinal preparations, in which the soluble and active principles of a medicine are extracted, leaving behind the insoluble and inert. Such are the waters, infusions, decoctions, tinctures, spirits, wines, vinegars, syrups, honeys, oxymels, fluid extracts, and oleoresins of the pharmacopoeias.

Waters. Aquae

3. Waters (aquae) are forms of solution which have been long in use, and which, with a somewhat peculiar signification, constitute a class of preparations in our Pharmacopoeia. Formerly, the name was somewhat indefinitely applied, embracing certain solutions of solid bodies, as lead-water, lime-water, tar-water, etc., and was occasionally extended in common language to spirituous preparations, as cologne-water, lavender-water, etc.; but, so far as it had a distinctive meaning, it was used to designate watery solutions of volatile substances, obtained by distillation; as mint-water, rose-water, etc. In the present Pharmacopoeia, the title Waters or Aquas is restricted to preparations in which volatile or gaseous substances are held in solution by water, no matter how the solution may be effected, whether by distillation with water, by simple trituration, or other method of impregnation; the condition being essential that the preparation might be made by distillation, as it often was originally. The medicines most frequently thus treated are the volatile oils of aro-matics, as of mint, cinnamon, fennel, etc.; but the category also embraces other medicines, as the waters of ammonia, carbonic acid, and chlorine; while solutions of non-volatile substances formerly called waters, as lime-water {aqua calcis) and potassa-water {aqua potasssae), are now designated as solutions (liquores).

Infusions. Infusa

4. Infusions (infusa) are aqueous solutions made by treating with water, without boiling, medicines containing principles soluble in water, with others insoluble. They are either cold or hot, the former being prepared with water at ordinary temperatures, the latter with the same liquid previously heated to the boiling point. Hot water acts more rapidly than cold under circumstances otherwise the same, and may, therefore, be preferred when speedy action is desirable. But it is sometimes objectionable in consequence of dissolving starchy matters, which are insoluble in cold water, and the presence of which may render the infusion more liable to speedy change. On the contrary, cold water is liable to the same objection in reference to vegetable albumen, which it dissolves, while hot water coagulates instead of dissolving it. Heat injuriously affects the virtues of certain medicines, and should not, therefore, be employed in preparing them. These considerations should be allowed some weight in the choice between cold and hot infusion. Many of the infusions are most elegantly and efficiently prepared by the process of percolation or displacement. The U. S. Pharmacopoeia uses both the method of percolation and that of simple maceration, preferring one or the other according to the nature of the substance used; and sometimes it presents the alternative of either method in reference to the same substance. Where percolation is used, the plan pursued is to moisten the medicine, in powder, with a little of the menstruum, then to pack it in a percolator, and pour on water till the infusion passed measures a given quantity, which is generally a pint. (See U. S. Dispensatory.) In domestic practice the method of maceration should generally be preferred; as that of percolation requires a degree of skill possessed only by the practical pharmaceutist.