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A naturally occurring metallic element. Potassium has an abundance in the earth's crust of 2.6%. It was discovered by Sir Humphrey Davy in 1807. Potassium is a soft, silvery-white metal that rapidly oxidizes in moist air. It does not occur in nature in the free state because it is highly reactive. It is found mainly as Potassium chloride (sylvite) and in clays (orthoclase, microcline). Major potassium salt deposits include the Great Salt Lake and Salduro Marsh in Utah and the Dead Sea between Israel and Jordan. Potassium salts are used to make fertilizer and hardened glass.

Synonyms and Related Terms

K; Kalium (Lat., Ned., Deut., Sven.); potassio (It.); Potássio (Port.); potasio (Esp.)


  • Dangerous fire risk.
  • May form explosive peroxides.
  • Reacts exothermically with water and moisture. Contact causes severe burns.
  • Fisher Scientific: MSDS

Physical and Chemical Properties

  • Soluble in liquid ammonia, aniline, mercury, and sodium.
  • Flame color is purple-red.
Composition K (atomic no. 19)
CAS 7440-09-7
Melting Point 63 C
Density 0.862 g/ml
Molecular Weight atomic wt = 39.0983
Boiling Point 770 C

Resources and Citations

  • Van Nostrand's Scientific Encyclopedia, Douglas M. Considine (ed.), Van Nostrand Reinhold, New York, 1976
  • Random House, Webster's Encyclopedic Unabridged Dictionary of the English Language, Grammercy Book, New York, 1997
  • The American Heritage Dictionary or Encarta, via Microsoft Bookshelf 98, Microsoft Corp., 1998
  • Richard S. Lewis, Hawley's Condensed Chemical Dictionary, Van Nostrand Reinhold, New York, 10th ed., 1993
  • The Merck Index, Martha Windholz (ed.), Merck Research Labs, Rahway NJ, 10th edition, 1983 Comment: entry 7763
  • G.S.Brady, Materials Handbook, McGraw-Hill Book Co., New York, 1971 Comment: p. 631

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