potassium nitrate, chemical compound, KNO₃, occurring as colorless, prismatic crystals or as a white powder; it is found pure in nature as the mineral saltpeter, or niter. (The name saltpeter is also applied to sodium nitrate, although less frequently.) It is slightly soluble in cold water and very soluble in hot water. Potassium nitrate is prepared commercially by the reaction of potassium chloride with sodium nitrate. When potassium nitrate decomposes (on heating) it releases oxygen; it has been used extensively as the oxygen-supplying component of gunpowder since about the 12th cent. It is also used in explosives, fireworks, model rocket propellants, matches, and fertilizers, as a preservative in foods (especially meats), and in the manufacture of nitric acid and of glass.

potassium hydroxide, chemical compound with formula KOH. Pure potassium hydroxide forms white, deliquescent crystals. For commercial and laboratory use it is usually in the form of white pellets. A strong base, it dissolves readily in water, giving off much heat and forming a strongly alkaline, caustic solution (see acids and bases). It is commonly called caustic potash. It closely resembles sodium hydroxide in its chemical properties and has similar uses, e.g., in making soap, in bleaching, and in manufacturing chemicals, but is less widely used because of its higher cost. It is prepared chiefly by electrolysis of potassium chloride; commercial grades of it sometimes contain the chloride as well as other impurities.

potassium hydrogen tartrate: see cream of tartar.

potassium chloride, chemical compound, KCl, a colorless or white, cubic, crystalline compound that closely resembles common salt (sodium chloride). It is soluble in water, alcohol, and alkalies. Potassium chloride occurs pure in nature as the mineral sylvite and is found combined in many minerals and in brines and ocean water. It is recovered (with other compounds) from the brine of Searles Lake in California. It is produced from sylvinite, a sodium chloride-potassium chloride mineral that is mined extensively near Carlsbad, N.Mex., and it is refined by fractional crystallization and by a flotation process. It is also recovered from lake brines in Utah and from ores in Saskatchewan, Canada. The chief use of potassium chloride is in the production of fertilizers; it is also used in chemical manufacture. For agricultural use it is often called muriate of potash; the concentration of potassium chloride in muriate of potash is expressed as a corresponding concentration of potassium oxide (K₂O), i.e., the concentration of potassium oxide that there would be if the potassium were present as its oxide instead of as its chloride. Thus, muriate of potash that contains (typically) 80% or 97% KCl by weight is said to contain 50% or 60% K₂O, respectively. Manure salts contain some potassium chloride.

potassium carbonate, chemical compound, K₂CO₃, white, crystalline, deliquescent substance that forms a strongly alkaline water solution. It is available commercially as a white, granular powder commonly called potash, or pearl ash. It was originally obtained from wood ashes or from the residue left in pots after certain plants, e.g., kelp, were burned in them. It is prepared commercially chiefly by electrolysis of potassium chloride to form potassium hydroxide, which is then carbonated (e.g., by adding carbon dioxide gas). It is used in the manufacture of soft soaps and glass, for washing wool, and in the production of other potassium compounds.

potassium, a metallic chemical element; symbol K [Lat. kalium=alkali]; at. no. 19; at. wt. 39.0983; m.p. 63.25°C;; b.p. 760°C;; sp. gr. .862 at 20°C;; valence +1.

Potassium is a soft, silver-white metal. Physically and chemically it resembles the other alkali metals in Group 1 of the periodic table. It is extremely reactive, more so than sodium. It combines so readily with oxygen that it is usually stored submerged in kerosene or some other hydrocarbon, out of contact with air. It reacts violently with water to form potassium hydroxide, KOH, releasing hydrogen, which usually ignites. It combines directly with the halogens, sulfur, and other nonmetallic elements (except nitrogen). It reacts with many organic compounds.

The metal has limited use since it so closely resembles sodium, which is readily available at lower cost. Nonetheless, potassium compounds are widely used in industry, although they are usually more expensive than the similar sodium compound. Potassium carbonate, or potash, K₂CO₃, is used principally in soap and glass manufacture. The chloride, KCl, is used in fertilizers and in the production of other potassium compounds. The chlorate, KClO₃, and perchlorate, KClO₄, are used in explosives and fireworks. The hydroxide, or caustic potash, KOH, is used in soaps. The nitrate, saltpeter (or niter), KNO₃, is used in matches and explosives. Other commercially useful compounds include the bromide, KBr, the cyanide, KCN, the chromate, K₂CrO₄, the dichromate, K₂Cr₂O₇, and the iodide, KI.

Javelle water contains potassium hypochlorite, KClO, a compound found only in solution. The metasilicate, K₂SiO₃, is used in water glass. Potassium has several useful tartaric acid salts, e.g., Rochelle salt (sodium potassium tartrate), tartar (argol) and cream of tartar (potassium hydrogen tartrate), and tartar emetic (potassium antimony tartrate). Potassium aluminum sulfate, KAl(SO₄)₂·12H₂O, is a compound used in tanning, in water purification, and in baking powder; usually called alum, it is also called potash alum to distinguish it from other alkali aluminum sulfates. Potassium permanganate, KMnO₄, a purple-black, crystalline compound that forms deep purple, aqueous solutions, is used in the chemical laboratory as a powerful oxidizing agent and in medicine as an antiseptic and disinfectant.

With sodium the metal forms alloys that are liquid at room temperature; these alloys are sometimes used in chemical reactions. Substances containing potassium impart a purple color to a flame. Potassium does not occur uncombined in nature but is found widely distributed in sylvite (KCl), carnallite (MgCl₂·KCl), feldspar, mica, and other minerals. It is the seventh most abundant element in the earth's crust and the sixth most abundant of the elements in solution in the oceans. It is found in mineral waters, brines, and salt deposits. Potassium is an essential nutrient for plants and animals.

Potassium metal is produced commercially by a thermochemical process in which molten potassium chloride is reacted with sodium vapor; this method is also used to produce liquid sodium-potassium alloys. The metal may be produced electrolytically from fused potassium hydroxide, but, unlike sodium and lithium, it reacts with carbon electrodes and may form explosive compounds. Potassium was discovered in 1807 by Humphry Davy, who decomposed potash with an electric current. Potassium was the first metal so discovered; Davy discovered sodium a few days later by a similar experiment.

Atomic Number:	Atomic Number: 19
Atomic Symbol:	Atomic Symbol: K
	Name of Element: Potassium
Atomic Weight:	Atomic Weight: 39.0983
Electron Configuration:	Electron Configuration: 2 · 8 · 8 · 1

Method for determining the age of igneous rocks based on the amount of argon-40 in the rock. Radioactive potassium-40 decays to argon-40 with a half-life of about 1.3 billion years, making this method useful for dating rocks that are billions of years old. A more sophisticated method, called argon-argon dating, provides a more accurate estimate of the original potassium-40 content by means of the ratio of argon-40 to argon-39 in the rock, thus yielding a more accurate age determination. Seealso dating.

Learn more about potassium-argon dating with a free trial on Britannica.com.

Chemical element, one of the alkali metals, chemical symbol K, atomic number 19. It is a soft, silvery white metal, not found free in nature and rarely used as the metal (except as a chemical reagent) because of its extreme reactivity. Potassium is essential for life and is present in all soils. Potassium ions (K⁺) and sodium ions act at cell membranes in electrochemical impulse transmission and in transport. Potassium in compounds has valence 1. The chloride is used as a fertilizer and a raw material for producing other compounds, and the hydroxide for making liquid soaps and detergents and in preparing various salts. The iodide is added to table salt to protect against iodine deficiency. The nitrate is also called saltpetre, and the carbonate is called potash.

Learn more about potassium with a free trial on Britannica.com.