The class emulsions comprises milk-like mixtures of liquids and solids. The term emulsion is restricted to oleaginous, fatty, or resinous bodies in a watery menstruum. The agents chiefly employed to emulsify fixed oils are the mucilages of acacia, tragacanth, chondrus, dextrin, yolk of egg, and sometimes tincture of quillaja; the latter, however, is somewhat toxic. Emulsions made with egg do not keep well. Acacia enters into the composition of most emulsions. Solutions of pancreatin or liquor potassae are rarely used. Emulsions of volatile oils may be made by rubbing the oil with some solid intended as an ingredient, or with sugar, syrup, or glycerin. If it be such an oil as oil of turpentine the emulsion may be improved by first mixing it with an equal bulk of a fixed oil, as olive oil, oil of sweet almond, or oil of sesamum, and afterwards proceeding as with the fixed oils. With the resins suspension is effected by means of mucilages; with the gum-resins water only is required, inasmuch as the mucilage thus formed by the gummy material of the gum-resin holds the resinous particles in suspension. Emulsions prepared by means of an alkaline emulsifier precipitate upon the addition of acids; emulsions prepared with mucilages or with the yolk of egg are precipitated by the addition of an excess of saline or alcoholic preparation, such as tinctures, wines, or fluid extracts. Emulsions, if properly prepared will not "crack," i. e., separate into oil and water upon standing. The National Formulary gives the following general directions for the preparation of emulsions:
Ɣ EMULSIONES (N. F.), Emulsions.—Formulary number, 123: "The successful formation of emulsions, whether of fixed or volatile oils, is most satisfactorily and expeditiously accomplished with acacia as the emulsifying agent. Hence, preference is given acacia in this Formulary, though other emulsifying agents are not ignored, and their use and application is exemplified in a number of alternative formulas for preparing emulsion of cod-liver oil.
Emulsification.—"When acacia is used as the emulsifying agent, it is important that the oil, the acacia, and the water, shall primarily be in absolutely definite proportion to each other by weight. This proportion is 8 parts of oil to 2 parts of acacia, and 3 parts of water. The oil (8), and acacia (2), in fine powder, are weighed into a mortar, and well mixed by trituration; the water (3), is then added in one portion, and the whole is triturated briskly until a thick, creamy emulsion is produced, the sides of the mortar being carefully scraped, and the mixture again triturated so as to insure the complete emulsification of all the oil. During warm weather, the water and oil should be cooled. The other ingredients may then be gradually added; first the flavoring, then the greater part of the water necessary to make the final quantity, then the syrup, etc. Finally, the quantity is adjusted by the addition of sufficient water. Alcoholic liquids should be added last, and should be previously mixed with a portion of the water. If these simple conditions and directions are carefully observed, and particularly, if the proportions by weight are accurate, a perfect emulsion is obtained with certainty and rapidity.
"With other emulsifying agents—mucilage of Irish moss, mucilage of dextrin, glycerite of egg, tincture of quillaja—the proportions need not be adjusted with the same minuteness. It suffices to place the emulsifier into a bottle or mortar, and to add the oil in small portions at a time, shaking or triturating briskly after each addition until emulsification is completed. Obviously, the preparation of this class of emulsions is very much facilitated by mechanical contrivances that are capable of producing brisk agitation and mingling of the two fluids, and such are necessarily resorted to when emulsions are to be made in large quantities for the market.
Ɣ B. Flavoring.—"Since no single or compound aromatic can be devised which would be acceptable under all circumstances as a flavoring for emulsion of cod-liver oil, the selection of the most suitable aromatic must be left to the prescriber or dispenser. Among those which are found to be most serviceable are the following, the quantities given below being intended for one thousand cubic centimeters (1000 Cc.) [33 fl℥, 391♏] of finished emulsion, though in some cases a smaller or a larger quantity, in the same proportion, may be preferable:
- Oil of gaultheria, four cubic centimeters (4 Cc.) [65♏].
- Oil of gaultheria, two cubic centimeters (2 Cc.) [32.5♏]; Oil of sassafras, two cubic centimeters, (2 Cc.) [32.5♏].
- Compound spirit of orange (U. S. P.), one and one-half cubic centimeters (1.5 Cc.) [24♏].
- Oil of gaultheria, two cubic centimeters (2 Cc.) [32.5♏]; oil of bitter almond, one-fourth cubic centimeter (0.25 Cc.) [4♏]; oil of coriander, one-fourth cubic centimeter (0.25 Cc.) [4♏].
- Oil of gaultheria, one and one-half cubic centimeters (1.5 Cc.) [24♏]; oil of sassafras, one and one-half cubic centimeters (1.5 Cc.) [24♏]; oil of bitter almond, one-fourth cubic centimeter (0.25 Cc.) [4♏].
- Oil of gaultheria, two and one-half cubic centimeters (2.5 Cc.) [41♏]; oil of bitter almond, two and one-half cubic centimeters (2.5 Cc.) [41♏].
- (7) Oil of neroli, one and one half cubic centimeters (1.5 Cc.) [24♏]; oil of bitter almond, one and one-half cubic centimeters (1.5 Cc.) [24♏]; oil of cloves, one-fourth cubic centimeter (0.25 Cc.) [4♏].
C. Preservation.—"When an emulsion of cod-liver oil is to be kept for some time, its deterioration may be prevented or retarded by the addition of sixty-five cubic centimeters (65 Cc.) [2 fl℥, 95♏] of alcohol in the place of the same quantity of water, when making one thousand cubic centimeters (1000 Cc.) [33 fl℥, 391♏] of emulsion."