EMULSIONS are mechanical mixtures of liquids that are immiscible under ordinary conditions, and which may be separated into layers on standing, heating, freezing, by agitation, the addi tion of other chemicals, etc. Familiar examples of emulsions are milk and butter—the first, an emulsion of oil in water; the latter an emulsion of water in oil. The term emulsion is also applied (although not with complete accuracy) to mechanical mixtures in which finely-divided solid particles are suspended in liquids in which they are insoluble. More properly, such mixtures are known as colloidal solutions or suspensoids. In dyeing, tanning, tinting of certain coloured glassware, water purification, etc., emulsions play an important part.
Froth flotation, by means of which many millions of tons of minerals annually are separated from their ores, employs emul sions of various vegetable and mineral oils (see METALLURGY). Basically, photography (q.v.) is also dependent on the use of emulsions, for dry plates and films are generally coated with gelatin emulsions.