Emulsions, Fr.; Emulsiones, G.; Emulsiones It; Sp
Under this head are included in the U. S. Pharmacopoeia liquid preparations in which oleaginous substances are suspended in aqueous fluids by the intervention of gum or other viscid matter. The preparations forming the present class of emulsions were termed Mixtures in earlier pharmacopoeias, and it is to be regretted that under this indefinite term are still grouped liquids of many kinds; the separation of these into proper classes is only a question of time, and the introduction of this new class into the Pharmacopoeia of 1890 marked the first step in the direction of greater accuracy in defining pharmaceutical preparations, and more system in classification. The object of emulsions is usually to facilitate the administration, to conceal the taste, or to obviate the nauseating effects of unpleasant medicines, and their perfection depends upon the intimacy with which the ingredients are blended. Some skill and care are requisite for the production of uniform and perfect emulsions. As a rule, the body to be suspended should be thoroughly mixed by trituration with the substance intended to act as the intermedium, before the aqueous vehicle is added. In the case of the liquid balsams and oils, if gum arabic is employed as the intermedium it should be previously brought to the state of mucilage of the consistence directed in the U. S. Pharmacopoeia. When a fixed oil, oleoresin, or balsam is to be made into an emulsion, the method most employed abroad is to add one part of gum to two or three of the oil, in a mortar, triturate until the mixture is complete, and then add at once twice as much water as gum used, and triturate rapidly until the oil is completely emulsified, then gradually add the remainder of the vehicle with constant trituration. Agitation in a bottle is sometimes substituted for trituration. The plan most largely used in this country is to make the emulsion with mucilage. Having a broad flat pestle and a mortar perfectly free from grease, put in a little mucilage, rub it around the mortar, add about half as much oil, triturate from the center so as to emulsify this, then add more mucilage, then oil, and so on until the operation is completed. Care is required never to get the oil in excess of the mucilage. This plan seems to accord with the principle laid down by R. Bother, that the most perfect and rapid emulsifier is a perfect emulsion. The proportion of gum and water necessary to make a good emulsion with the fixed oils varies with the oil. Thus, while castor oil requires only two drachms of the gum and three drachms of water to the ounce, most other fixed oils require half their weight of gum, and a weight of water equal to half that of the oil and gum united. These quantities being well rubbed together, any desirable amount of water may afterwards be gradually added, and will readily incorporate with the other ingredients. The white of egg has been frequently ordered by physicians as the suspending substance, but it is inferior for this purpose to the yolk, or to gum arabic. When the white is used it should be well beaten, and incorporated with the oleaginous or balsamic substances before the water is added. When volatile oils are to be emulsified they should be mixed with an equal volume of inert fixed oil to promote stability. Quillaja, saponin, and other substances having similar properties have been proposed as emulsifying agents, but they are objectionable on account of their medicinal activity. Emulsifying agents should be inert.
Leo Boon (J. A. Ph. A., 1916, v, 496) gives an extensive review of the literature on emulsification and Roon and Oesper have made an important contribution to the theory of emulsification (J. I. & E. C. 1917, p. 156). The authors agree with Fischer [Science 1916, p. 468) that emulsification is due to, or accompanied by, the formation of a hydrated colloid compound. Both the English and Continental methods of emulsification were studied carefully. The unsatisfactory results obtained by the majority of workers with the English method, are alleged to be due to the fact that the hydration of the emulsifying agent occurs progressively and not all at one time and for the greater part is not accomplished in the presence of the internal phase (oil). In the Continental method all of the emulsifying agent (colloid) is hydrated at one time and in the presence of the internal phase (oil). After experimenting with various proportions of materials, it is stated by the authors that the best and quickest results are obtained by the use of the following proportions in the preparation of the original nucleus: oil 4, water 3, gum 2.
Experimental emulsions were produced of the following substances: hexane, sp. gr. 0.691; chloroform, sp. gr. 1.526; carbon tetrachloride, sp. gr. 1.597; benzene, sp. gr. 0.877; oil of turpentine, sp. gr. 0.85; mineral oil, sp. gr. 0.853; cottonseed oil, sp. gr. 0.921. Gum emulsions and soap emulsions we're made of all these and the conclusions, in part, were as follows:
- The presence of a hydrated colloid is necessary for emulsification.
- This hydration compound is most efficiently used if formed at the moment of dispersion of the internal phase—in other words, the three constituents, internal phase, emulsifier and water, in critical proportions, must all be mixed at one time in order to form a properly hydrated nucleus.
- Slight variations from the proper procedure or from the critical proportions yield either less stable emulsions or none at all.
- No emulsion results if the emulsifier is diluted before the dispersion of the internal phase.