Potassium
Potassium is an alkali metal element denoted by the atomic symbol K. It has an atomic number of 19, and an atomic weight of 39.0983. It is a soft, silvery-white metal that is brittle at low temperatures. Potassium melts at 145.9°F (63.28°C) and it becomes a gas at it boiling point of 1398.2°F (759°C).
For centuries before elemental potassium was identified, people made use of its compounds. Potassium carbonate, for example, which is found in the ashes of burned wood, is often called potash. This compound was first used by the ancient Romans to make soap. The Chinese used a naturally occurring mineral called saltpeter (potassium nitrate) to make gunpowder. During the 1700s, American colonists made soap, glass, and other products using potassium carbonate derived from wood ashes. To produce just a ton of this chemical required the burning of several acres' worth of timber. In the early 1800s, a cheaper substitute for potassium carbonate became available-- sodium carbonate, which began to be manufactured via the Leblanc process. This temporarily halted depletion of America's forests.
In certain processes, sodium can be substituted for potassium because the two elements have very similar properties. Both are very soft, silvery-white metals belonging to the alkali metals group. Although both are highly reactive, potassium is more reactive than sodium. When a lump of potassium is dropped into water, the reaction quickly releases hydrogen, which ignites from the heat of the reaction and explodes. Potassium will even react violently with ice at temperatures as low as -148°F (-100°C). Potassium oxidizes quickly in air, forming a surface film; if the air is moist, the metal can burst into flames. For this reason, potassium has to be stored in containers of kerosene or other liquids that prevent its exposure to air or oxygen.
Because of its high reactivity, potassium does not generally exist as a free element in nature. However, potassium compounds are widely distributed in underground ores, mainly sylvinite and carnallite, which contain potassium chloride. By weight, 2.4 percent of the Earth's crust consists of potassium, making it the seventh most abundant element. Potassium is also found in seawater, but in smaller concentrations than sodium and other dissolved elements. Potassium is lighter than all other metals except lithium. It also has a fairly low melting point (145.9°F [63.28°C]).
Before electricity became available to chemists as an experimental tool, pure potassium could not be obtained, because its compounds are difficult to break apart. In 1807 potassium became the first element to be discovered by electrolysis. Sir Humphry Davy isolated the metal by passing an electric current through molten potassium hydroxide. According to many sources, Davy danced happily around the room when his experiment succeeded. The chemical name Davy gave to the metal was later changed by a German chemist to the name kalium (evidently derived from the Arabic qali, "alkali"), which is why potassium's chemical symbol is K. Although Davy's electrolytic process produced only small amounts of potassium, greater quantities were obtained a few years later. Joseph Gay-Lussac and Louis Thenard discovered a chemical method of producing potassium by heating the molten hydroxide with red-hot iron.
Potassium's role in plant and animal life began to be recognized in 1847, when Justus von Liebig found potassium in living tissues. Since then, scientists have discovered that potassium is present in all living cells. Potassium compounds are found in the ashes of wood, seaweed, and all other organic substances. In animals, certain amounts of potassium are essential to the function of muscles. Too much of the element, however, causes muscles to enter a state of permanent relaxation, called potassium inhibition. Potassium makes up about 0.4 percent of the human body. In fact, humans are very slightly radioactive due to the tiny amount of a potassium isotope contained in our tissues. The growth of plants also depends on potassium, which is found in many fertile soils. The main use of potassium chloride is in the manufacture of fertilizers. For plants that cannot tolerate much chloride, potassium sulfate fertilizers are used.
Potassium compounds are used for a variety of applications. Although fertilizers are the most important product containing potassium, fireworks and gunpowder are manufactured from potassium nitrate. This compound and other potassium salts give flames a violet color. Potassium nitrate is also used as a fertilizer and meat preservative. Some matches also contain potassium compounds. Potassium carbonate is still used to make soap and glass, though methods have been much improved since even colonial American days. Other potassium compounds are used as dyes, additives to consumer products, catalysts, and medicines.
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