Emulsions are liquid preparations consisting of oily, fatty, resinous, or otherwise insoluble substances suspended in watery liquids by the intervention of gum, mucilage, or other viscid matter. The object of emulsifying a substance is to render it easily miscible with water.

For the internal administration of Oils it is often necessary to exhibit them in a palatable form, so that they may be borne by the stomach and their assimilation favored. This is usually effected by suspending the oil in a watery liquid or mixture by means of an emulsifying agent, such as acacia, etc.

Many natural substances are intimate mixtures of oils or fats with water, in the form of an emulsion. Of animal products, Milk is a most perfect emulsion; so is Egg-yolk. From the Milk-juice of some plants the water evaporates and the dried milk-juice collects in portions of the plant or exudes from them when wounded; in this way the gum-resins of asafcetida, etc., are produced. From these substances Emulsions may be obtained by restoring the water lost by evaporation - that is, by rubbing them with water in a mortar. In this way the so-called natural Emulsions are made.