Mixture

A mixture is matter containing two or more substances physically combined without fixed chemical proportions. Its components retain their chemical identities and can often be separated by physical methods.

Pure substance: Matter with a fixed composition and characteristic chemical properties, consisting of one chemical substance. Unlike a mixture, a pure substance has a fixed composition rather than variable component proportions.
Filtration: A separation method that passes a fluid through a porous medium to retain suspended particles. Filtration separates insoluble solids from fluids in heterogeneous mixtures.
Air: The mixture of gases surrounding Earth, composed chiefly of nitrogen and oxygen. Air is a familiar homogeneous mixture whose gas proportions are not chemically fixed.
Chemical reaction: A process that transforms reactants into products through changes in chemical bonds. Mixing alone need not cause the bond changes that define a chemical reaction.
Aristotle: An ancient Greek philosopher whose works shaped Western accounts of nature, matter, and change. His theories of elements and combination framed early explanations of mixed materials.
Chemical compound: A pure substance whose elements are chemically bonded in fixed proportions. Compounds have fixed elemental ratios; mixtures do not impose fixed proportions on their components.
Distillation: A separation method that vaporizes and condenses substances according to differences in volatility. Different boiling behavior allows distillation to separate components of some mixtures.
Alloy: A material containing a metal and one or more additional elements, typically combined to improve properties. Alloys are solid mixtures whose components produce useful mechanical or chemical properties.
Homogeneous mixture: A mixture with uniform composition and properties throughout at the relevant scale. This subtype contrasts with mixtures whose components occupy visibly distinct regions.
Robert Boyle: A seventeenth-century natural philosopher whose experimental work helped establish modern chemistry. Boyle distinguished mixtures from compounds and challenged inherited theories of matter.

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