As a solid, the alkali is deliquescent and readily absorbs moisture and carbon dioxide from the air. It dissolves easily in water, and makes the water warm when this happens. Sodium hydroxide is used as a solution called lye to make soap. Lye is also used to unclog drains. Its dissolving properties and its ability to easily break surface tension are fundamental for its uses. It works in two ways. First, it combines with grease to make soap. Second, it dissolves hair (which is soluble in any basic solution).