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The common name for the natural mixture of gases surrounding the earth. Air, or atmosphere, predominately contains Nitrogen (75-78 %) and Oxygen (21-23 %). Trace levels of other gases (Argon, Carbon dioxide, Neon, Helium, Methane, etc.) are also present along with varying amounts of water vapor. The index of refraction of air is 1.0003. Air is the primary source for the manufacture of pure gases (oxygen, nitrogen, etc.). It is also used as a coolant, as a blowing agent, and as a filler in flotation devices.

Synonyms and Related Terms

Luft (Deut.); air (Fr.); ar (Port.)


Noncombustible; but necessary for combustion.

Physical and Chemical Properties

Melting Point -216.2 to -191.3 C
Density 1.00 g/ml
Refractive Index 1.0003
Boiling Point -194.3 C

Resources and Citations

  • The American Heritage Dictionary or Encarta, via Microsoft Bookshelf 98, Microsoft Corp., 1998
  • G.S.Brady, Materials Handbook, McGraw-Hill Book Co., New York, 1971
  • Susan E. Schur, Conservation Terminology: A review of Past & Current Nomenclature of Materials, Technology and Conservation, Spring (p.34-39); Summer (p.35-38); Fall (p.25-36), 1985