This section is from the book "Experimental Cookery From The Chemical And Physical Standpoint", by Belle Lowe. Also available from Amazon: Experimental cookery.
Clayton states that two very distinct classes of emulsions exist. (1) The very dilute emulsions. These emulsions are simple emulsions, containing only oil and water. In this class only the oil in water emulsions are known. (2) The concentrated emulsions. The more concentrated emulsions may be either of two types according to whether the oil or the water is the dispersed phase. In the (1) oil-in-water type of emulsion the drops of oil are the dispersed or divided phase. In the (2) water-in-oil type of emulsion the water is the dispersed phase. The factors determining the type of emulsion formed will be considered later.