These are prepared from Venice turpentine, guaiacum resin, resin of jalap, and such-like substances.

Venice turpentine is easily emulsified by its own weight of gum acacia or by yolk of egg (two yolks to 20 grammes).

Resin of guaiacum is finely powdered and rubbed in a mortar with half its weight of gum acacia, water being added gradually. This emulsion assumes a bluish tint, varying in intensity according to the degree of concentration. The blue gradually changes to a green. A few drops of sweet spirit of nitre will develop the blue tint, as will also exposure to the air.

Resin of jalap is sometimes combined with almonds into an emulsion (four blanched sweet almonds to 1 gramme of resin), but it soon separates. If neither almonds nor egg be ordered, but only gum or sugar, it is generally best to rub the resin first with its own weight of spirit before mixing with water.

Quinoidine and some other amorphous alkaloids, tannate of quinine, oleo-resins of cina, male fern, and cubebs may be conveniently treated like resins. By rubbing them with three or four times their weight of sugar, and adding spirit of wine to make a thin electuary, they mix well with water. Without the addition of spirit these substances are apt to form a sediment which is very difficult to mix evenly by shaking.

Emulsions of Essential Oils, such as oil of turpentine, do not last long. They are best formed by brisk shaking with a thick mucilage. They require about ten times their weight of gum acacia or one yolk of egg for 5 to 10 grammes of essential oil. [One yolk will emulsify more if the operation is carefully done.-Ed.]

Camphor should be rubbed to a fine powder with the aid of a few drops of absolute alcohol, then mixed with ten times its weight of gum acacia or the yolk of an egg to 5 grammes (gum in preference), and the water added gradually. Any oil or balsam in the mixture should be mixed with the camphor before the gum is added. Syrup should be mixed up with the powder before the addition of water.