Degree to which a substance dissolves in a solvent to make a solution (usually expressed as grams of solute per litre of solvent).
Solubility of one fluid (liquid or gas) in another may be complete (totally miscible; e.g., methanol and water) or partial (oil and water dissolve only slightly). In general, "like dissolves like" (e.g., aromatic hydrocarbons dissolve in each other but not in water). Some separation methods ( absorption , extraction) rely on differences in solubility, expressed as the distribution coefficient (ratio of a material's solubilities in two solvents). Generally, solubilities of solids in liquids increase with temperature and those of gases decrease with temperature and increase with pressure. A solution in which no more solute can be dissolved at a given temperature and pressure is said to be saturated (see saturation ). See also Joel Hildebrand .