Soap-suds penetrate fabrics more completely than water alone, and when the soap comes in contact with fatty material, it emulsifies it, that is, very finely divides it into minute particles, so that it can be easily removed.
"Ontario Teachers' Manuals: Household Management"
Ministry of Education
Kerosene emulsifies grease and makes it easy to rinse away.
"School and Home Cooking"
Carlotta C. Greer
Egg is another material which emulsifies fats.
"School and Home Cooking"
Carlotta C. Greer