Oil-in-water $\frac{O}{W}$: oil droplets dispersed in water. Examples: milk, vanishing cream. Emulsifier: sodium stearate, proteins. Can be diluted with water. Water-in-oil $\frac{W}{O}$: water droplets dispersed in oil. Examples: butter, cold cream. Emulsifier: long-chain alcohols (cetyl alcohol), lanolin. Can be diluted with oil. Test to distinguish: add water-soluble dye — if it colours the dispersion medium, it's O/W. Or add oil-soluble dye. Demulsification: breaking emulsion by heating, centrifuging, freezing, or adding chemical demulsifier.