BASIC DEFINITIONS ON HOW TO MAKE EMULSIONS

When two liquids are immiscible but do not separate immediately they are said to form an emulsion. Some emulsions are quite stable and will take a long time to separate. For example milk is an emulsion of water and fat but is fairly stable. Other emulsions may separate quite quickly, for example a simple salad dressing of oil and vinegar will separate almost immediately (note that vinegar is water based).
The emulsion itself consists of small droplets of one liquid within the body of a second liquid. An emulsion containing droplets of oil in water is called an oil-in-water emulsion and the oil is called the dispersed phase while the water is called the continuous phase. An emulsion with droplets of water in oil is called a water-in-oil emulsion. A good oil-in-water emulsion will consist of very fine oil droplets homogeneously dispersed throughout the body of water.
Since colas are oil-in-water emulsions this discussion of emulsions assumes that an oil phase is being dispersed within a water phase. In practice neither the water phase nor the oil phase of an emulsion are likely to be pure substances. For example in colas the continuous water phase is an acidic solution of citric or phosphoric acid together with other ingredients such as caramel and sugar, the oil phase is a complex mixture of organic molecules from the essential oil flavourings. In general the water soluble molecules all stay in the water phase and the oil phase will be a mixture of all the liquid molecules that are not soluble in water (i.e. a mixture of oils).
FOR COMPLETE ARTICLE GO TO: http://sparror.cubecinema.com/cube/cola/chemistry/cola1.htm#top