POTASSIUM (REVISED)

Note: This article, originally published in 1998, was updated in 2006 for the eBook edition.

Overview

Potassium is one of the alkali metals. The alkali metals are the elements that make up Group 1 (IA) of the periodic table. The periodic table is a chart that shows how chemical elements are related to one another. The alkali metals also include lithium, sodium, rubidium, cesium, and francium. They are among the most active metals.

Potassium is so active that it never occurs free in nature. It always occurs in compounds, combined with other elements. It was first prepared in pure form in 1807 by English chemist Sir Humphry Davy (1778-1829). Davy used a new method of isolating elements that he had invented, electrolysis. In electrolysis, an electric current is passed through a molten (melted) compound. The electrical current breaks the compound into its elements. (See sidebar on Davy in the calcium entry in Volume 1.)

There are very few uses for potassium as a pure element. However, compounds of potassium have many important applications, the most important of which is as a fertilizer.

SYMBOL
K

ATOMIC NUMBER
19

ATOMIC MASS
39.0983

FAMILY
Group 1 (IA)
Alkali metal

PRONUNCIATION
poe-TAS-see-um

Discovery and naming

Early humans were familiar with potash, a potassium compound that forms when wood burns. Wood ashes were washed with water to dissolve the potash. It was then recovered by evaporating the water. Potash was often called vegetable alkali. That name comes from the origin of the material ("vegetable" plants that contain wood) and the most important property of the material, alkali. The word alkali means a strong, harsh chemical that can be used for cleaning. Common household lye (such as Drano) is a typical alkali.

The chemical name for potash is potassium carbonate (K₂CO₃). Early humans also knew about a similar substance called mineral alkali. This material was made from certain kinds of rocks. But it also had alkali properties. "Mineral alkali" was also called soda ash. The modern chemical name for soda ash is sodium carbonate (Na₂CO₃).

For many centuries, people had trouble telling "vegetable alkali" and "mineral alkali" apart. The two materials looked and acted very much alike. For example, they could both be used as cleaning materials. The main difference between them was the source from which they came. It was not until the eighteenth century that chemists understood the difference between potash (vegetable alkali) and soda ash (mineral alkali).

By the late 1700s, chemists were reasonably sure that both potash and soda ash contained elements they had never seen. They tried to think of ways to break these compounds down into their elements. The first method that Davy tried was to pass an electric current through a water solution of one compound or the other. But no new element was ever formed. What Davy did not know was how active the elements potassium and sodium are. Both elements are freed when an electric current is passed through a water solution of potash or soda ash. But as soon as the element is formed, it reacts immediately with the water. The free element can never be recovered by this method.

Then Davy thought of another way to separate potash and soda ash into their elements. He decided to use no water in his experiment. Instead, he melted a sample of potash and a sample of soda ash. Then he passed an electric current through the molten (melted) substances. He was amazed to see a tiny liquid droplet of metal formed in each case. The droplet was the first piece of potassium and sodium ever to be seen by a human.

Davy had his first success with potassium using this approach on October 6, 1807. A few days later he repeated his experiment with soda ash and produced pure sodium metal. Davy named these two elements after their much older names: potassium for "potash" and sodium for "soda ash."

Physical properties

Potassium is a soft, silvery-white metal with a melting point of 63°C (145°F) and a boiling point of 770°C (1,420°F). Its density is 0.862 grams per cubic centimeter, less than that of water (1.00 grams per cubic centimeter). That means that potassium metal can float on water. Chemically, though, that's not a good idea (see "Chemical properties" below).

The melting point of potassium is very low for a metal. It will melt over the flame of a candle flame.

Chemical properties

Like the other alkali metals, potassium is very active. It reacts with water violently and gives off hydrogen gas:
So much heat is produced in this reaction that the hydrogen gas actually catches fire and may explode. Floating potassium metal on the surface of water is not a good idea! In that instance, the potassium would skip along the surface of the water. The skipping is caused by hydrogen gas produced in the reaction pushing the metal around. The potassium would soon catch fire, burn, and, perhaps, explode.

Potassium reacts readily with all acids and with all non-metals, such as sulfur, chlorine, fluorine, phosphorus, and nitrogen.

Occurrence in nature

Potassium is the eighth most abundant element in the Earth's crust. Its abundance is estimated to be about 2.0 to 2.5 percent. It is just slightly less abundant than its alkali cousin, sodium.

Potassium is less dense than water, so it can float on water. However, chemically, potassium reacts with water violently. It will give off hydrogen and eventually catch fire.

Potassium occurs widely in many different minerals. Some of the most important of these are sylvite, or potassium chloride (KCl); sylvinite, or sodium potassium chloride (NaCl KCl); carnallite, or potassium magnesium chloride (KCl MgCl₂); langbeinite, or potassium magnesium sulfate (K₂SO₄ • 2MgSO₄); and polyhalite, or calcium magnesium potassium sulfate (2CaSO₄ • MgSO₄ • K₂SO₄).

Isotopes

There are three naturally occurring isotopes of potassium, potassium-39, potassium-40, and potassium-41. Potassium-40 is radioactive. Isotopes are two or more forms of an element. Isotopes differ from each other according to their mass number. The number written to the right of the element's name is the mass number. The mass number represents the number of protons plus neutrons in the nucleus of an atom of the element. The number of protons determines the element, but the number of neutrons in the atom of any one element can vary. Each variation is an isotope.

About ten artificial radioactive isotopes of potassium are known also. A radioactive isotope is one that breaks apart and gives off some form of radiation. Artificially radioactive isotopes are produced when very small particles are fired at atoms. These particles stick in the atoms and make them radioactive.

Potassium-40 is of special interest to scientists. Potassium is widely distributed in nature in plants, animals, and rocks. That means that nearly everything on Earth contains at least a tiny amount of radioactive potassium-40. That includes the human body! About 0.012 percent of the potassium in the human body is radioactive potassium-40. However, that is not enough radiation to cause any harm.

Radioactive potassium-40 in rocks can be used to measure the age of objects. When the isotope gives off radiation, it breaks down to an isotope of argon:
A scientist can analyze a rock to see how much potassium-40 and how much argon-40 it contains. The older the rock, the more argon-40 and the less potassium-40 it contains. The younger the rock, the more potassium-40 and the less argon-40 it contains.

One might wonder why argon gas does not escape into the atmosphere. The answer is that argon gas is trapped within the solid rock. It is released only when the potassium-dating process is conducted.

Extraction

The word "potash" is still a widely used term for potassium compounds taken from the earth. But it no longer means potassium carbonate to most people. It can mean potassium sulfate (K₂SO₄), potassium chloride (KCl), potassium nitrate (KNO₃), potassium hydroxide (KOH), or potassium oxide (K₂O). People cling to "potash" because it is the term used in the manufacture of fertilizers. And fertilizers are far and away the most important use of potassium compounds today.

Chemistry and the environment

E nvironmentalists often say that everything in nature is related. Here is a good example of that principle:

Potash was a widely used material in Colonial America. People used the compound to make soap, glass, and dozens of other products. At the time, potash was easy to get. All one had to do was burn a tree and collect potash from its ashes.

The only problem was that a single tree does not produce much potash. To get all the potash a family might need, one might have to burn dozens or hundreds of trees. Colonists did not worry too much about this problem. America in the 1700s was covered with trees. Few people thought about or cared about "saving the environment." If they ran out of trees, they just moved farther west.

One can imagine what America would have looked like if Colonists continued this practice. Fortunately, they did not have to. In the 1780s, French chemist Nicolas Le Blanc (1742-1806) invented an inexpensive method for making soda ash. Le Blanc's method used salt, or sodium chloride (NaCl); limestone, or calcium carbonate (CaCO₃); and coal (pure carbon). These three materials are all common and inexpensive. The Le Blanc method of making soda ash is quick, easy, and cheap. Before long, soda ash had become one of the least expensive chemicals made artificially. In the United States, trees were no longer burned to get potash.

The most important source of potash in the United States is a mine near Carlsbad, New Mexico, that produces sylvinite (KCl NaCl). That mine produces about 85 percent of the potash mined in the United States. Potash is also produced from huge long-buried salt mine blocks formed when ancient seas evaporated (dried up). In Michigan, for example, potash is obtained by passing water into these mines. The water returns to the surface and is allowed to evaporate. Potassium compounds in the mine remain behind when the water has all evaporated.

Potassium metal is produced by combining potassium chloride with sodium metal at high temperatures. But this method is of little interest because potassium metal has few uses.

Uses

Potassium metal is sometimes used as a heat exchange medium. A heat exchange medium is a material that picks up heat in one place and carries it to another place. Potassium metal is sometimes used as a heat exchange medium in nuclear power plants. There, heat is produced at the core, or center, of the reactor. Liquid potassium is sealed into pipes surrounding the core. As heat is given off, it is absorbed (taken up) by the potassium. The potassium is then forced through the pipes into a nearby room. In that room, the potassium pipes are wrapped around pipes filled with water. The heat in the potassium warms the water. Eventually the water gets hot enough to boil. It changes into steam and is used to operate devices that generate electricity.

Compounds

By far the most important compound of potassium is potassium chloride (usually referred to as "potash," of course!). At least 85 percent of that compound is used to make synthetic (artificial) fertilizers. In 1996, about 1.5 billion kilograms (3.4 billion pounds or 1.7 million tons) of potassium chloride was produced in the United States for use in fertilizers.

Many other potassium compounds are commercially important, although no use begins to compare with the amount of potash used for fertilizers. Some examples of other important potassium compounds are the following:

Potassium is one of the three primary nutrients, or macronutrients, required by plants.

potassium bicarbonate, or baking soda (KHCO₃): baking powders; antacid (for upset stomach); food additive; soft drinks; fire extinguishers

potassium bisulfite (KHSO₃): food preservative (but not in meats); bleaching of textiles and straw; wineand beer-making; tanning of leathers

potassium bitartrate, or cream of tartar (KHC₄H₄O₆): baking powder; "tinning" of metals; food additive

potassium bromide (KBr): photographic film; engraving

potassium carbonate, or potash (K₂CO₃): specialized glasses and soaps; food additive

potassium chromate (K₂CrO₄): dyes and stains (bright yellowish-red color); explosives and fireworks; safety matches; tanning of leather; fly paper

potassium fluorosilicate (K₂SiF₆): specialized glasses, ceramics, and enamels; insecticide

potassium hydroxide, or caustic potash (KOH): paint remover; manufacture of specialized soaps; fuel cells and batteries; bleaching; food additive; herbicide

potassium nitrate, or nitre, or saltpeter (KNO₃): explosives, fireworks, matches, rocket fuel; manufacture of glass; curing of foods potassium pyrophosphate, or tetrapotassium pyrophosphate, or TKPP (K₄P₂O₇): soaps and detergents

potassium sodium tartrate, or Rochelle salt (KNaC₄H₄O₆): baking powder; medicine; silvering of mirrors

Health effects

Potassium is essential to both plant and animal life. It is one of the three primary nutrients, or macronutrients, required by plants. Plants require relatively large amounts of potassium in order to grow and remain healthy.

Potassium plays a number of important roles in the human body also. It helps control the proper balance of fluids in cells and body fluids. It is involved in the transmission of chemical messages between nerve cells and in the contraction of muscles. Potassium also helps in the digestion of food and in the proper function of the eyes. In many of these reactions, potassium and sodium work together to keep these functions performing properly.

The average human who weighs 70 kilograms (150 pounds) has 140 grams (5 ounces) of potassium in his or her body. Normal daily intake of potassium is about 3.3 grams (0.1 ounce). Since potassium occurs in all plants, humans normally do not have any problems getting enough of the element in their daily diet.

Potassium

Description

Potassium is one of the electrolytes essential to the smooth running of the human body; in fact just about all bodily functions depend on it to some extent. It is also one of the most abundant minerals in the body, constituting 70% of the positive ions inside cells; the rest are a mixture of sodium, magnesium, calcium, arginine , and others. Potassium is distributed to the cells by a process of passive diffusion and is regulated by an enzyme called adenosinetriphosphatase together with the level of sodium concentration inside the cell. Potassium and sodium are antagonistic, which means that an imbalance of one will automatically cause an imbalance of the other; normally potassium should predominate inside the cell.

General use

Potassium is necessary for normal cell respiration; a deficiency can cause decreased levels of oxygen, which will reduce the efficiency of cell function. Adequate supplies of potassium are also required to regulate heartbeat, facilitate normal muscle contraction, regulate the transfer of nutrients to cells, and regulate kidney function and stomach juice secretion, among other things. One of the most important uses of potassium in the body is in the process of nerve transmission, as it is a cofactor catalyst for the activation of several enzyme systems, but since only minute amounts are required for these processes, deficiency in this respect is unlikely.

Potassium is thought to be therapeutically useful in many ways, including assisting in the treatment of alcoholism, acne , alleviating allergies , promoting the healing of burns , and preventing high blood pressure. It can also help with such problems as congestive heart failure, chronic fatigue syndrome , or kidney stones . People suffering from any of the above should consider increasing their intake of potassium after talking to a professional.

Symptoms of potassium deficiency

A deficiency of potassium in the blood is referred to as hypokalemia and manifests itself in many ways. Among the most serious are arthritis, high blood pressure, heart disease, stroke, cancer , and even infertility , as potassium constitutes a vital element of seminal fluid.

Potassium deficiency will increase acid levels in the body, lowering the natural pH, which will have far reaching effects. Lack of potassium can also aggravate problems caused by lack of protein. If potassium levels are down, the liver cannot operate normally, particularly regarding transformation of glucose to glycogen. A healthy liver should have about twice as much potassium as sodium.

Potassium deficiency can cause problems with the formation of connective tissue, and can render normally strong body tissue vulnerable to all kinds of problems. The collagen of a healthy person is approximately as strong as steel, and the strength of bone tissue can be likened to that of cast iron . Lack of potassium may create a susceptibility to fractures , skin lesions that do not heal, or other connective tissue problems. So important is potassium for the protection of collagen that many natural health gurus claim that along with other vital nutrients, it constitutes an essential element of protection against premature aging . As long ago as the 1920s, Max Gerson was the first person ever to cure lupus lesions with a diet designed to reduce abnormally high sodium levels and raise potassium levels to normal, which was entirely raw fruit and vegetables.

Potassium is essential to the efficient processing of foods in the body; without it they cannot be broken down into the proper compounds. This can lead to rheumatism, and is one reason why adequate potassium prevents rheumatism.

Potassium requirements

In the past potassium was more plentiful in the diet than salt, but gradually, the situation has been reversed. The widespread lack of potassium in modern diets is largely due to modern processing and high levels of salt added to most processed foods. Cooking and processing destroy potassium, and added salt further robs the body of vital potassium. This departure from traditional cooking of fresh homegrown fruit and vegetables is likely the cause of many health problems faced by modern society.

Who needs potassium supplements?

Those who may need to take potassium supplements include women who take oral contraceptives, abusers of alcohol or drugs, smokers, athletes, workers whose job involves physical exertion, patients who have had their gastrointestinal tract surgically removed, anyone suffering from any degree of malabsorption syndrome, and vegetarians. People who have eating disorders, especially bulimia and anorexia, are particularly at risk from damage due to low potassium levels. Also, individuals who have been ill, anyone who has undergone surgery and those who are taking cortisone or digitalis preparations, and those suffering from high levels of stress will probably also have low potassium levels.

No RDA has been officially established for potassium, but practitioners recommend that the optimal daily intake should be in the region of 3,500 mg. The average daily intake is about 2,500 mg. However, in general, nutritionists recommend reducing salt intake and ensuring adequate supply by increasing the amount of fresh fruit and vegetables in the diet.

If a person feels that he or she may be suffering from a potassium deficiency, but would like to make sure before taking supplements, there are a variety of laboratory tests that can be conducted. They include serum-potassium determinations (although these may be unreliable unless levels are very low), serum creatinine, electrocardiograms, serum-pH determinations, whole blood, sublingual cell smears, and red blood cell potassium level determinations.

Preparations

Absolutely the best sources of potassium are fresh natural foods. Supplements may have side effects and large doses must be taken to approach the levels of potassium that can be obtained from food; the average tablet contains about 90 mg, for example, and a medium banana contains 500 mg. Vegetables containing the highest levels of potassium are generally those containing the lowest levels of starch. Seaweed has an amazingly high potassium content, containing roughly ten times as much as leafy vegetables, but also contains a large amount of mineral salt. Green coconut milk is another source of potassium.

Plentiful sources of potassium

There is a great variety of natural foods that are an excellent source of potassium. These include avocados; bananas; chard; citrus fruits; juices such as grapefruit, tomato, and orange; dried lentils; green leafy vegetables; milk; molasses; nuts such as almonds, brazils, cashews, peanuts, pecans and walnuts; parsnips; dried peaches; potatoes; raisins; sardines; spinach; and whole-grain cereals.

Cooking

Boiling food in water is a sure way to lose the potassium in it, unless it is to make soup. Baking and broiling are ways in which food can be cooked while at the same time preserving the potassium content, indeed, these methods preserve all the nutrients apart from vitamin C and some of the B vitamins which are destroyed by heat. Broiling also oxidizes essential fatty acids . Stir-frying is also a good way of preserving nutrients. It is important to vary the intake of potassium rich foods in order to ensure adequate intake of other nutrients and to avoid the possibility of toxicity, as some vegetables contain elements that are toxic if they are eaten in large amounts (oxalic acid in rhubarb for example). It is important to note that freezing also depletes potassium levels in foods.

RECIPE FOR POTASSIUM BROTH. Many variations are to be found under the heading "potassium broth," and most natural health practitioners recommend one version or another, but the main constituents are the following vegetables, generally any vegetable of choice can be added to this base.

Ingredients

• 2 lb potatoes
• 1 lb carrots
• 1/2 lb peas
• bones for stock, or a vegetable bouillon cube
• 4 oz cracked wheat or pearl barley

First, in a stainless steel pan, boil the stock bones, if using them. After about one hour, add the remaining ingredients and continue to simmer in plenty of water for about another hour. It is preferable to use the potatoes and carrots well scrubbed, but with their skins on, as this retains valuable nutrients. Keep any unused soup in the refrigerator.

Potassium supplements

Potassium supplements come in either tablet or liquid form, and anything over 390 mg needs a prescription in the United States. Enteric coated tablets have been known to cause ulcers, as they do not dissolve until they reach the intestines and may prove too concentrated for the undefended intestinal wall. To be on the safe side, supplements should be taken with a glass of juice. Slow-release enteric-coated supplements are now available, which decrease the danger of ulcers. Potassium gluconate is the ideal supplement, as it more closely resembles the potassium found in plants. Small divided doses should be taken, as opposed to one large dose, when treating a potassium deficiency. Athletic drinks are an electrolyte replacement and as such contain potassium. Potassium supplements should be kept in a cool, dry place, out of direct light. They should not be frozen and should not be kept in the bathroom medicine cabinet as heat and moisture may reduce effectiveness.

Precautions

In general, the multitude of nutrients that humans require in order to stay healthy are synergistic, which means they are interdependent. If depleted of one, it is highly likely that there are deficiencies in others. Many nutrients, for example, require the presence of either calcium or vitamin C for efficient use by the body, and if suffering from a deficiency of any of the B vitamins, there is almost certainly a deficiency in the B vitamins in general, as they occur together in nature. With this in mind, it is very unwise to take large amounts of any one nutrient without making sure that the full spectrum of nutrients is plentifully available for the body to make use of. This can best be achieved by making sure that a large proportion of the daily diet is in the form of raw fruit and vegetables, whole grains, and unroasted nuts.

Of all the essential nutrients that are commonly taken as supplements, potassium is perhaps the most dangerous. Only 14 grams of potassium can cause death under certain circumstances, particularly when intake is low at other times, as it has been found that when potassium intake is restricted, somehow the mechanism for utilizing it is altered, so that large amounts cannot be processed.

Just the right amount of potassium is essential. Too much or too little can cause muscle spasms and cramps if a calcium deficiency also exists. With this in mind, it is important to ensure adequate intake of calcium and vitamin D , which will promote the uptake of calcium in the body.

Many sufferers of degenerative diseases such as tuberculosis , cancer, and arthritis, suffer from high serum potassium levels. This is not because they have too much serum, but because the disease affects body functions in such a way that it throws off this valuable nutrient instead of using it. In such cases, natural sources of potassium, such as fresh fruit or vegetable juice, can be more effective than supplements.

Potassium and heart disease

Potassium has been implicated in the treatment of heart disease since the 1930s, but some heart disease that is due to malnutrition does not respond to potassium. Indeed, because of the impaired ability of the body to take up potassium, it can be dangerous. Most heart disease patients of the Western world, however, can benefit from an increase in potassium levels.

Potassium and arthritis

For many, when they begin to eat a well balanced selection of fresh vegetables and fruits, and eliminate a large proportion of processed, denatured foods, they begin to feel amazingly well very quickly, as the potassium/sodium balance in the body is restored. Tiredness and other symptoms, such as arthritis, are soon replaced with renewed energy and vigor, and the body is able to replenish itself and finds new strength. However, potassium is only partially successful at treating osteoarthritis .

Side effects

Those who are taking potassium-sparing diuretics, such as spironolactone, triamterene, or amiloride should not take potassium supplements. Anyone allergic to potassium supplements or those who have kidney disease should not take them either. Those suffering from Addison's disease, heart disease, intestinal blockage, stomach ulcers, those using medication for heart disease, or taking diuretics, or who are above the age of 55, should consult a doctor before taking potassium supplements. There are no contradictions for pregnant or breast feeding women, although they should not take mega-doses.

ECG and kidney function tests can be affected by potassium supplementation, the doctor should be informed if potassium supplements are being taken. However, supplementation will not affect blood tests, unless they are to measure serum-potassium levels.

Symptoms of potassium overdose

Overdose symptoms of potassium include listlessness, mental confusion, tingling of limbs, weakness, pallid complexion, low blood pressure, and an irregular or fast heartbeat. These symptoms can progress to a drop in blood pressure, convulsion, coma, and eventually cardiac arrest, and can also be triggered by any kind of shock to the system. If any of the above symptoms occur, or in cases of bloody stool (may appear black and tarry), or difficulty in breathing or nausea , medical help should be sought immediately. High serum-potassium is the major problem with shock and is the major cause of death in cases of shock or injury. This is a life-threatening situation, and self treatment is not appropriate.

If such an emergency occurs and medical help is not available, a glass of water containing half a teaspoon of salt, a quarter of a teaspoon of bicarbonate soda and a little honey will help. Potassium supplements should be taken with extreme care in cases of dehydration, as this can be fatal. Adequate liquids, particularly juice, should always accompany the supplement.

Interactions

Care should be taken when taking potassium supplements in conjunction with diuretics. A practitioner should be consulted. A doctor should be informed when a patient is taking potassium supplements. In addition, the following are known to react with potassium:

• Amilorid: causes a dangerous rise in blood potassium.
• Atropine: increases the possibility of intestinal ulcers, which may be caused by potassium supplements.
• Belladonna: increases possibility of intestinal ulcers.
• Calcium: increases likelihood of heartbeat irregularities.
• Captopril: increases likelihood of potassium overdose.
• Digitalis preparations: may cause irregular heartbeat.
• Enalapril: increases chance of overdose.
• Laxatives: may decrease effectiveness of potassium (due to the fact that they leach potassium from the body).
• Spironolactone: increases blood potassium.
• Triamterene: increases blood potassium.
• Vitamin B₁₂ : slow release supplements may decrease the absorption of vitamin B₁₂, increasing requirements.

Resources

BOOKS

Gerson, Max. A Cancer Therapy. California, Totality books: 1977.

OTHER

Weber, Charles. "Roles of Potassium in the Body." http://www.members.tripod.com/~charles_W/arthritis4.html.

"Potassium." In Vitamins Plus.com. http://www.vitaminsplus.com/library/minerals/potassium.asp.

Patricia Skinner

Potassium

melting point: 63.38°C
boiling point: 759°C
density: 0.862 g/cm³
most common ions: K⁺

Potassium is a soft, silvery alkali metal that reacts strongly with water to produce hydrogen gas. The word "potassium" is derived from "potash" or "pot ashes," as Humphry Davy isolated the element in 1807 via the electrolysis of caustic potash, KOH. The element's symbol is derived from kalium (Latin), which originated from qali (Arabic for "alkali"). Currently, potassium metal is generated by the reduction of molten potassium chloride, KCl, with sodium and the use of fractional distillation to separate the resulting mixture. In nature it is never found in its elemental form. Compounds of potassium are found primarily in the minerals sylvite, carnallite, langbeinite, and polyhalite, as well as in the brines of the Dead Sea in Jordan and the Great Salt Lake in Utah. Potassium is the second most abundant alkali metal and the eighth most abundant element in Earth's crust (18,400 ppm). Potassium burns violet in the flame test.

The industrial demand for potassium metal is much smaller than that for sodium. Potassium-sodium alloys (which are liquid at room temperature) serve as heat-exchange liquids in the cooling systems of nuclear reactors. Strong bases such as potassium amides and alkoxides are formed from the reaction of potassium with amines and alcohols, respectively.

Compounds of potassium are economically more important than the metal. KCl is used extensively in fertilizers. KOH is used to make liquid soaps and detergents. Potassium nitrate, KNO₃, serves primarily as an oxidizing agent in gunpowder and pyrotechnics. Potassium superoxide, KO₂, is used in backup ventilation equipment as it generates oxygen gas in the presence of CO₂. Potassium ions are essential to plants and animals as many metabolic reactions and pathways depend on their presence.

see also Alkali Metals.

Nathan J. Barrows

Bibliography

Emsley, John (2001). Nature's Building Blocks: An A-Z Guide to the Elements. New York: Oxford University Press.

Greenwood, N. N., and Earnshaw, A. (1997). Chemistry of the Elements, 2nd edition. Boston: Butterworth-Heinemann.

Lide, David R., ed. (2000). CRC Handbook of Chemistry & Physics, 81st edition. New York: CRC Press.

potassium (symbol K) Common metallic element first isolated in 1807 by English chemist Sir Humphry Davy. Its chief ores are sylvite, carnallite and polyhalite. Chemically it resembles sodium. Potassium in the form of potash is used as a fertilizer. The natural element contains a radioisotope K⁴⁰ (half-life 1.3 × 10⁹ yr), which is used in the radioactive dating of rocks. Properties: at.no. 19; r.a.m. 39.102; density 0.86; m.p. 63.65°C (146.6°F); b.p. 774°C (1425°F); most common isotope K³⁹ (93.1%). See also alkali metals

potassium (K) An element that is required for healthy plant growth. Potassium ions neutralize anionic macromolecules and organic acids and thus control the water potential of cells. They pass readily through membranes and are important in the movements of leaves and guard cells. A potassium deficiency leads to reduced growth and to dark or blue-green coloration in the leaves, which may also develop a purple brown pigment.