Note: This article, originally published in 1998, was updated in 2006 for the eBook edition.
Sulfur belongs to the chalcogen family. Other members of the family are oxygen, selenium, tellurium, and polonium. These elements make up Group 16 (VIA) of the periodic table. The periodic table is a chart that shows how chemical elements are related to each other.
The term chalcogen comes from two Greek words meaning "ore forming." An ore is a naturally occurring mineral used as a source for an element. Many ores are compounds of a metal and oxygen or a metal and sulfur. Compounds that contain two elements, one of which is sulfur, are called sulfides. For example, a beautiful gold-colored mineral is called pyrite, or "fool's gold," because it looks so much like real gold. Pyrite is iron sulfide (FeS2).
Sulfur was known to ancient peoples. Its physical and chemical properties are very distinctive. It often occurs as a brilliant yellow powder. When it burns, it produces a clear blue flame and a very strong odor.
Group 16 (VIA)
Sulfur, also spelled as sulphur, is a very important element in today's world. Its most important use is in the manufacture of sulfuric acid (H2SO4). There is more sulfuric acid made than any other chemical in the world. It has an enormous number of important uses.
Discovery and naming
Sulfur must have been well known to ancient peoples. They sometimes referred to it as brimstone. Sulfur sometimes occurs in bright yellow layers on the top of the earth. It has a sharp, offensive odor. When it burns, it gives off a strong, suffocating smell. The odor is like that produced when a match is struck.
The Bible mentions brimstone in a number of places. For example, Sodom and Gomorrah were two towns destroyed by God for the wicked ways of their citizens: "The Lord rained upon Sodom and upon Gomorrah brimstone and fire."
But ancient people certainly did not think about sulfur the way modern chemists do. In fact, they used the word "element" to talk about anything that was basic. Ancient Greek philosophers, for example, thought that everything consisted of four elements: earth, fire, water, and air. Other philosophers thought there were only two elements: sulfur and mercury.
But early thinkers were often confused as to what they meant by the word "sulfur." They often were talking about anything that burned and gave off large amounts of smoke. To them, "sulfur" was really a "burning substance." It took centuries for scientists to identify sulfur as an element.
Sulfur exists in two allotropic forms. Allotropes are forms of an element with different physical and chemical properties. The two forms of sulfur are known as α-form and β-form (the Greek letters alpha and beta, respectively). Both allotropes are yellow, with the α-form a brighter yellow and the β-form a paler, whitish-yellow. The α-form changes to the β-form at about 94.5°C (202°F). The α-form can be melted at 112.8°C (235.0°F) if it is heated quickly. The β-form has a melting point of 119°C (246°F). The boiling point of the α-form is 444.6°C (832.3°F).
The two allotropes have densities of 2.06 grams per cubic centimeter (α-form) and 1.96 grams per cubic centimeter (β-form). Neither allotrope will dissolve in water. Both are soluble in other Liquids, such as benzene (C6H6), carbon tetrachloride (CCl4), and carbon disulfide (CS2).
Another allotrope of sulfur is formed when the element is melted. This allotrope has no crystalline shape. It looks like a dark brown, thick, melted plastic.
Sulfur's most prominent chemical property is that it burns. When it does so, it gives off a pale blue flame and sulfur dioxide (SO2) gas. Sulfur dioxide has a very obvious strong, choking odor.
Sulfur sometimes occurs in bright yellow layers on the top of the earth. It has a sharp, offensive odor.
Sulfur also combines with most other elements. Sometimes it combines with them easily at room temperature. In other cases, it must be heated. The reaction between magnesium and sulfur is typical. When the two elements are heated, they combine to form magnesium sulfide (MgS):
Sulfur also combines with hydrogen gas:
The compound formed in this reaction is hydrogen sulfide (H2S). Hydrogen sulfide has one of the best known odors of all compounds. It smells like rotten eggs. Hydrogen sulfide is added to natural gas (methane) used in homes for cooking and heating. Methane is odorless. So the unique smell of hydrogen sulfide makes it easy to know when there is a methane leak.
Occurrence in nature
At one time, sulfur occurred in layers along the Earth's surface. They were easy for humans to find and take. Deposits like these are more difficult to find today. One place they still occur is in the vicinity of volcanoes. Sulfur is released from volcanoes as a gas. When it reaches the cold air, it changes back to a solid. It forms beautiful yellow deposits along the edge of a volcano.
Large supplies of sulfur still occur underground. They are removed by the Frasch process (see accompanying sidebar).
Sulfur also occurs in a number of important minerals. Some examples are barite, or barium sulfate (BaSO4); celestite, or strontium sulfate (SrSO4); cinnabar, or mercury sulfide (HgS); galena, or lead sulfide (PbS); pyrites, or iron sulfide (FeS2); sphalerite, or zinc sulfide (ZnS); and stibnite, or antimony sulfide (Sb2S3).
The abundance of sulfur in the Earth's crust is thought to be about 0.05 percent. It ranks about number 16 among the elements in terms of their abundance in the earth. It is more abundant than carbon, but less abundant than barium or strontium.
The largest producers of sulfur in the world are the United States, Canada, China, Russia, Mexico, and Japan. In 1996, the United States produced about 11,800,000 metric tons of sulfur. It is mined in 30 states, Puerto Rico, and the U.S. Virgin Islands.
There are four naturally occurring isotopes of sulfur: sulfur-32, sulfur-33, sulfur-34, and sulfur-36. 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.
Sulfur occurs in the vicinity of volcanoes.
Six radioactive isotopes of sulfur are known also. A radioactive isotope is one that breaks apart and gives off some form of radiation. Radioactive isotopes are produced when very small particles are fired at atoms. These particles stick in the atoms and make them radioactive.
One radioactive isotope of sulfur, sulfur-35, is used commercially. In medicine, the isotope is used to study the way fluids occur inside the body. It also has applications in research as a tracer. A tracer is a radioactive isotope whose presence in a system can easily be detected. The isotope is injected into the system at some point. Inside the system, the isotope gives off radiation. That radiation can be followed by means of detectors placed around the system.
As an example, a company that makes rubber tires might want to know what happens to the sulfur added to tires. Sulfur-35 is added to rubber along with non-radioactive sulfur. Researchers follow the radioactive isotope in the tires to see what happens to the sulfur when the tires are used.
The Frasch method of removing sulfur
T he Frasch method is one of the most famous mining systems ever invented. It was developed by German-American chemist Herman Frasch (1851-1914) in 1887.
The Frasch method is based on the low melting point of sulfur. The element melts at a temperature slightly higher than that of boiling water (100°C). Here is how the method works:
A set of three nested pipes (one inside each other) is sunk into the ground. The innermost pipe has a diameter of about an inch. The middle pipe has a diameter of about four inches. And the outer pipe has a diameter of about eight inches.
A stream of superheated water is injected into the outer pipe. Superheated water is water that is hotter than its boiling point, but that has not started to boil. Superheated water can be made by raising the pressure on the water. Its temperature can reach 160°C (320°F).
The superheated water passes down the outer pipe into the underground sulfur, causing it to melt. The molten (melted) sulfur forms a lake at the bottom of the pipe.
At the same time, a stream of hot air under pressure is forced down the innermost (one-inch) pipe. The hot air stirs up the molten sulfur and hot water at the bottom of the pipe. A foamy, soupy mixture of sulfur and water is formed. The mixture is forced upward through the middle pipe. When it reaches the surface, it is collected. The sulfur cools and separates from the water.
Similar applications of sulfur-35 involve studying sulfur in steel when it is made, seeing how sulfur affects the way engines operate, following what happens when proteins (which contain sulfur) are digested, and learning how drugs that contain sulfur are processed in the body.
Like coal, sulfur sometimes occurs in thick layers under ground. One way to remove sulfur would be to mine it the way coal is mined. But a much easier method for removing sulfur from the ground is the Frasch method (see accompanying sidebar).
Sulfur has relatively few uses as an element. One of the most important of those uses is in vulcanization. Vulcanization is the process of adding sulfur to rubber to make it stiff and hard. It keeps the rubber from melting as it gets warmer. The discovery of vulcanization by Charles Goodyear (1800-60) in 1839 is one of the greatest industrial accomplishments of modern times.
Some powdered sulfur is also used as an insecticide. It can be spread on plants to kill or drive away insects that feed on the plants. By far the majority of sulfur is used, however, to make sulfur compounds. The most important of these is sulfuric acid (H2SO4).
Nearly 90 percent of all sulfur produced goes into sulfuric acid. Sulfuric acid is the number one chemical in the world in terms of the amount produced. Each year, almost twice as much sulfuric acid is made as the next highest chemical, nitrogen. In 1996, more than 45 million tons of sulfuric acid were produced in the United States alone.
The greatest portion, nearly 75 percent, of sulfuric acid is used to make fertilizers. The next most important use, 10 percent, is in the petroleum industry. Other important uses of sulfuric acid are in the treatment of copper ores; the production of paper and paper products; the manufacture of other agricultural chemicals; and the production of plastics, synthetic rubber, and other synthetic materials.
Vulcanization is the process of adding sulfur to rubber to make it stiff and hard.
Sulfuric acid is also used in smaller amounts to make explosives, water treatment chemicals, storage batteries, pesticides, drugs, synthetic fibers, and many other chemicals used in everyday life.
The cleansing power of sulfur has been known for many centuries. At one time, ancient physicians burned sulfur in a house to cleanse it of impurities. Creams made with sulfur were used to treat infections and diseases. In fact, sulfur is still used to treat certain medical problems. Sulfur is prepared in one of three forms. Precipitated sulfur (milk of sulfur) is made by boiling sulfur with lime. Sublimed sulfur (flowers of sulfur) is pure sulfur powder. And washed sulfur is sulfur treated with ammonia water. Washed sulfur is used to kill parasites (organisms that live on other organisms) such as fleas and ticks. It is also used as a laxative, a substance that helps loosen the bowels.
Sulfur is a macronutrient for both plants and animals. A macronutrient is an element needed in relatively large amounts to insure the good health of an organism. Sulfur is used to make proteins and nucleic acids, such as DNA. It also occurs in many essential enzymes. Enzymes are chemicals that make chemical reactions occur more quickly in cells. Humans usually have no problem getting enough sulfur in their diets. Eggs and meats are especially rich in sulfur.
A person who does not get enough sulfur in his or her diet develops certain health problems. These include itchy and flaking skin and improper development of hair and nails. Under very unusual conditions, a lack of sulfur can lead to death. Such conditions would be very rare, however.
The cleansing power of sulfur has been known for many centuries.
Plants require sulfur for normal growth and development. When plants do not get enough sulfur from the soil, their young leaves start to turn yellow. Eventually, this yellowing extends to the whole plant. The plant may develop other diseases as a result.
Sulfur—the tenth most abundant element in the universe—is the nonmetallic chemical element of atomic number 16. It has a symbol of S, an atomic weight of 32.07, and a specific gravity of 2.07 (rhombic form) or 1.96 (monoclimic form). Sulfur boils at 832.5°F (444.7°C) and consists of four stable isotopes of mass numbers 32 (95.0%), 33 (0.75%), 34 (4.2%) and 36 (0.015%). Sulfur atoms found in different locations have slightly different percentages of the four isotopes, however.
Sulfur is a bright yellow solid that can exist in many allotropic forms with slightly different melting points, all around 239°F (115°C). The two main forms are called rhombic sulfur and monoclinic sulfur. There is also a rubbery, non-crystalline form, called plastic or amorphous—without shape—sulfur. An ancient name for sulfur is brimstone, meaning burning stone. It does indeed burn in air with a blue flame, producing sulfur dioxide:
Sulfur itself has no odor at all, but it has a bad reputation because it makes many smelly compounds. Sulfur dioxide is one of them; it has a sharp, choking, suffocating effect on the unfortunate breather. The reference to fire and brimstone in the Bible was one of the worst punishments that its authors could think of. The fact that sulfur comes from deep under the ground and that sulfur dioxide can be smelled in the fumes of volcanoes further fueled people’s imaginations of what Hell must be like.
Sulfur makes up only 0.05% of the Earth’s crust, but it is easy to get because it occurs uncombined as the element, S8 (eight sulfur atoms tied together into each molecule of the element and joined in a ring).
Sulfur occurs in huge, deep underground deposits of almost pure element, notably along the Gulf Coast of the United States and in Poland and Sicily. However, miners do not have to go underground to get it. They make the sulfur come to them by a clever arrangement of three pipes within pipes, drilled down into the sulfur bed. This arrangement is called the Frasch process. Superheated steam is shot down through the outermost pipe to melt the sulfur. (The steam has to be super-heated because sulfur does not melt until 239°F [115°C], which is hotter than steam.) Then, compressed air is shot down the innermost pipe, which forces the liquid sulfur up and out the middle pipe.
Sulfur is also widely distributed in the form of minerals and ores. Many of these are in the form of sulfates, including gypsum (calcium sulfate, CaSO4• H2O), barite (barium sulfate, BaSO4) and Epsom salts (magnesium sulfate, MgSO4• 7H2O). Others are metal sulfides, including iron pyrites (iron sulfide, FeS2), galena (lead sulfide, PbS), cinnabar (mercuric sulfide, HgS), stibnite (antimony sulfide, Sb2S3) and zinc blende (zinc sulfide, ZnS). The sulfur is recovered from these metal ores by roasting them—heating them strongly in air, which converts the sulfur to sulfur dioxide. For example,
Then the sulfur dioxide can go directly into the manufacture of sulfuric acid, which is where more than 90% of the world’s mined sulfur winds up.
Some sulfur is used directly as a fungicide and insecticide, in matches, fireworks, and gunpowder, and in the vulcanization of natural rubber. Most, however, is converted into a multitude of useful compounds.
Sulfur is in group 16 of the periodic table, directly below oxygen. It can form compounds in any one of its three major oxidation states:−2,+4, or+6.
Sulfuric acid is the parent acid of all sulfate compounds. Among the most important sulfates is calcium sulfate (CaSO4), which occurs naturally as gypsum, alabaster, and selenite. Copper sulfate is used as an agricultural insecticide and to kill algae in water supplies. Alums are double sulfates of aluminum and another metal such as potassium, chromium, or iron. The most common alum is potassium aluminum sulfate, KAl(SO4)2• 12H2O. In water, it makes a gelatinous, goopy precipitate of aluminum hydroxide, Al(OH)3, which, when it sinks to the bottom, carries along with it all sorts of suspended dirt, leaving behind clear water. Alum is therefore used in water purification.
Hydrogen sulfide is the parent acid of the sulfides, a family of compounds that contain nothing but sulfur and a metal. This family includes many metal ores, including iron pyrites, galena, cinnabar, stibnite, and zinc blende, as mentioned above, plus sulfides of copper and silver. Other sulfides are used in leather tanning, as pesticides, and in depilatories—creams that remove unwanted hair from the hides of cattle and from people.
Hydrogen sulfide itself is a foul-smelling gas. When eggs and certain other animal matter go rotten and putrefy, the stench is mostly hydrogen sulfide. It is often present in flatus—expelled intestinal gas. Hydrogen sulfide is extremely poisonous, but fortunately, it smells so bad that people do not hang around long enough to be overcome by it. Other very bad-smelling compounds of sulfur are the mercaptans, a family of organic sulfur-containing compounds. A mercaptan is the major ingredient in the aroma of skunks. A tiny amount of a gaseous mercaptan is deliberately added to the natural gas that is used for home heating and cooking, so that dangerous gas leaks can bedetectedby smell. Natural gas itself is odorless.
Sulfur is a macronutrient for both plants and animals. It is used primarily to make proteins and nucleic acids. Sulfur-deficiency disorders are very rare, but not unheard of. For example, abnormally low levels of sulfur can cause itchy and flaking skin and improper development of hair and nails. In plants, a deficiency of sulfur can cause the young leaves on a plant to begin turning yellow.
Ede, Andrew. The Chemical Element: A Historical Perspective. Westport, CT: Greenwood Press, 2006.
Emsley, John. Nature’s Building Blocks: An A-Z Guide to the Elements. Oxford: Oxford University Press, 2002.
Lide, D.R., ed. CRC Handbook of Chemistry and Physics Boca Raton, FL: CRC Press, 2005.
Merck. The Merck Index. Whitehouse Station, NJ: Merck; London: Harcourt, 2001.
Siekierski, Slawomir. Concise Chemistry of the Elements. Chichester, UK: Horwood Publishing, 2002.
Robert L. Wolke
Sulfur is a homeopathic remedy that is used to treat a variety of chronic or acute ailments. Elemental sulfur is present in all living tissues. Sulfur is often referred to as brimstone or flowers of sulfur.
Sulfur was used during biblical times as a remedy for skin disorders such as acne and scabies . Flowers of sulfur were burned to disinfect the rooms of persons with infectious disease. Sulfur was also taken with molasses as an internal cleanser, and was used to treat chronic bronchitis, constipation , and rheumatism. In the early 2000s the element is used in the manufacture of dyes, gunpowder, insecticides, fungicides, sulfuric acid, and rubber (as a hardening agent).
Sulfur is known as the king of homeopathic remedies because it has such a wide range of use. It works well with almost every other remedy and it acts on many different maladies and ailments. This polychrest has a deep, long-lasting effect on the body and is often used to bring out symptoms for further treatment. For this reason, sulfur is generally used to treat chronic ailments, although it is also used for acute conditions such as fevers and colds. Sulfur stimulates the body's natural healing powers, causing a general improvement of symptoms and sometimes causing new symptoms.
Homeopaths prescribe sulfur to treat skin ailments such as herpes, rashes, psoriasis, eczema , and acne. Other conditions helped by this remedy include arthritis, colds, coughs, flatulence, gastrointestinal disturbances, and headaches.
Ailments are caused by loss of vital fluids, drug abuse, overeating, becoming chilled, a change from cold to warm weather, effects of a debilitating disease, or from suppression of skin eruptions, hemorrhoids , or bodily discharges.
Typical sulfur patients are fair-haired, blue-eyed persons with red faces and lips that become cracked when they are ill. Their tongues often have a white coating and are red around the edges and on the tip. They are lean, stoop shouldered, lazy, averse to bathing, untidy, and disorderly. They don't pay attention to what they are wearing and often walk around with unmatched socks or missing ties. Patients are oversensitive to odors, especially their own, which are usually smelly.
Sulfur patients have often been called the "ragged philosopher," referring to the patient's disorderly ways. For instance, a sulfur type might be an inventor or scholar who is so absorbed in his project that he forgets to wash or change clothes. Patients are very bright but they spend a lot of time wandering about and studying strange subjects. They are dreamers and philosophers who lack perseverance to see their dreams through to fruition. They start many projects but complete few.
Physical symptoms include excessive thirst, swollen glands, profuse sweat, sensitivity to heat, burning pains, hot feet, boils , and acne. Symptoms generally appear on the left side. Bodily discharges are hot, burning, and sour smelling. The patient is extremely intolerable of the cold and other weather conditions. Arthritis, coughing, and hoarseness of the throat are all caused by damp weather or a change in weather. Skin conditions are often caused by a change in weather.
These patients are very sensitive to food and the times they eat. If a meal is delayed they may become nauseous and weak. At 10 a.m. or 11 a.m. they get an empty feeling in their stomachs and feel an intense hunger. Patients generally suffer from indigestion and other gastrointestinal disorders. They crave alcohol, sweets, spicy foods, fatty foods, and stimulants, but dislike milk and meat. Bread, cold food or drinks, fats, milk, and sweets aggravate their systems.
Mentally, patients are irritable, critical, discontented, impatient, depressed, quarrelsome, restless, hurried, anxious, easily offended, fearful, timid, absent-minded, sad, and weepy. They would rather not work; their symptoms often occur as a result of physical or mental exertion. The patient is always tired and lacks endurance. If made to stand for long periods of time he may feel faint.
Symptoms are aggravated by bathing, cold air, motion, itching, fasting , heat, milk, or standing. They are worse from 10-11 a.m., after eating, or in a stuffy room. Symptoms such as headaches may recur on a regular basis, i.e. every seven or ten days. Patients are worse after a long sleep and may not want to get up. All sulfur symptoms are better from fresh air and warm drinks.
The backache typical of sulfur is aching, sore, and stiff. The back feels weak, tired, and bruised. It is worse from standing or walking, after sitting for long periods, during menstruation , or at night.
Sulfur patients catch colds easily and often. They cannot become overheated, remain in a cold place, or overexert themselves without catching a cold. The sulfur cold is accompanied by smelly nasal discharge, congestion, sneezing , eye inflammations, and an itchy, dry nose that, when blown, may bleed.
The sulfur cough is generally dry in the evening and loose in the morning. The chest is congested and the sides hurt from coughing. There is a feeling of dust in the throat. The discharge that is expectorated from the cough is of a greenish color. Patients may often awake from coughing. The cough is better when the patient is exposed to open air.
Diarrhea that occurs early in the morning around 5 a.m. is indicative of sulfur. The diarrhea is painless, slimy, watery, and foul smelling. It is accompanied by flatulence and is somewhat relieved by expulsion of the gas .
Earaches are accompanied by aching and lacerating pains. The earache is worse in the left ear. There is a ringing or roaring noise in the ear. The ears are frequently plugged and itchy.
Eye inflammations often accompany a cold. The eyes are itchy, watery, burning, dry, and sensitive to light. The eyelids itch in the daytime only. The patient may wake up with his eyes glued shut. Washing them, however, aggravates the condition.
Fatigue is worse in the evening or from talking. It is caused by sun exposure, hunger, or walking.
Fevers are hot and are accompanied by chills , shivering, and sweating. They are worse in the evening, after waking, or from mental exertion. The feet become extremely hot; therefore, the patient may stick his feet out from under the bedcovers to cool them.
The patient is very gassy and suffers from gas that smells like rotten eggs. The stomach is bloated and rumbles in irritation. The gas is often accompanied by a burning sensation and offensive-smelling stools.
Headaches are confined to the forehead or top of the head. They are hot and burning with hammering pains. These congestive headaches are caused by damp weather and are accompanied by nausea and vomiting . They often occur on Sunday and recur periodically. They are aggravated by motion, cold drinks, eating, bending over, blowing the nose, coughing, rising in the morning, and sneezing. Sometimes stars, zigzags, or other shapes will appear before the eyes.
Indigestion is common in sulfur patients. The patient can digest almost nothing, but he can't go long without eating. He has a weak stomach and a slow digestion. Stomach pains are sensitive to touch and a heavy feeling is present in the stomach. The patient is hungry at 10 a.m. and may need to eat to avoid feeling faint or weak. She may get a headache if she doesn't eat at that time. Indigestion is accompanied by sour belches, gas that smells rotten, bloating, and burning pains. It is worse after eating or from drinking milk.
Insomnia is caused by frequent waking in the early morning hours (3-5 a.m.). For this reason, the patient has a tendency to sleep late. However, no matter how much sleep the patient has, he always wakes up feeling tired. Short catnaps taken throughout the day refresh the patient. Patients are often unable to sleep before midnight.
Skin conditions are itchy, intense, and worse at night or in warm beds. The skin is itchy and burning and chaps easily. Ailments include herpes, rashes, acne, eczema, psoriasis, and dermatitis .
The sore throat is accompanied by swollen tonsils, burning pains, and a hoarse voice upon waking. The throat is dry and raw and may feel dusty. The throat is worse from coughing and swallowing.
The homeopathic remedy is created by adding pure sulfur powder to a water/alcohol mixture or by grinding it with milk sugar. The mixture is then diluted and succussed to create the final preparation.
Sulfur is available at health food and drug stores in various potencies in the form of tinctures, tablets, and pellets.
If symptoms do not improve after the recommended time period, a homeopath or health care practitioner should be consulted.
The recommended dose should not be exceeded.
There are no side effects but individual aggravations may occur.
When taking any homeopathic remedy, use of peppermint products, coffee, or alcohol is discouraged. These products may cause the remedy to be ineffective.
Sulfur should not be taken immediately before lycopodium .
Cummings, Stephen, M.D., and Ullman Dana, M.P.H., Everybody's Guide to Homeopathic Medicines. New York, NY: Jeremy P. Tarcher/Putnam, 1997.
Sulfur is the non-metallic chemical element of atomic number 16. It has a symbol of S, an atomic weight of 32.07, and a specific gravity of 2.07 (rhombic form) or 1.96 (monoclimic form). Sulfur boils at 832.5°F (444.7°C) and consists of four stable isotopes of mass numbers 32 (95.0%), 33 (0.75%), 34 (4.2%) and 36 (0.015%). Sulfur atoms found in different locations have slightly different percentages of the four isotopes, however.
Sulfur is a bright yellow solid that can exist in many allotropic forms with slightly different melting points, all around 239°F (115°C). The two main forms are called rhombic sulfur and monoclinic sulfur. There is also a rubbery, non-crystalline form, called plastic or amorphous—without shape—sulfur. An ancient name for sulfur is brimstone, meaning "burning stone." It does indeed burn in air with a blue flame, producing sulfur dioxide :
Sulfur itself has no odor at all, but it has a bad reputation because it makes many smelly compounds. Sulfur dioxide is one of them; it has a sharp, choking, suffocating effect on the unfortunate breather. The "fire and brimstone" of the Bible was one of the worst punishments that its authors could think of. The fact that sulfur comes from deep under the ground and that sulfur dioxide can be smelled in the fumes of volcanoes further fueled people's imaginations of what Hell must be like.
Where sulfur is found
Sulfur makes up only 0.05% of the Earth's crust, but it is easy to get because it occurs uncombined as the element, S8 (eight sulfur atoms tied together into each molecule of the element and joined in a ring).
Sulfur occurs in huge, deep underground deposits of almost-pure element, notably along the Gulf coast of the United States and in Poland and Sicily. However, miners do not have to go underground to get it. They make the sulfur come to them by a clever arrangement of three pipes within pipes, drilled down into the sulfur bed. This arrangement is called the Frasch Process. Superheated steam is shot down through the outermost pipe to melt the sulfur. (The steam has to be superheated because sulfur doesn't melt until 239°F [115°C], which is hotter than "regular" steam.) Then, compressed air is shot down the innermost pipe, which forces the liquid sulfur up and out the middle pipe.
Sulfur is also widely distributed in the form of minerals and ores. Many of these are in the form of sulfates, including gypsum (calcium sulfate , CaSO4 • 2H2O), barite (barium sulfate , BaSO4) and Epsom salts (magnesium sulfate , MgSO4 • 7H2O). Others are metal sulfides, including iron pyrites (iron sulfide, FeS2), galena (lead sulfide, PbS), cinnabar (mercuric sulfide, HgS), stibnite (antimony sulfide, Sb2S3) and zinc blende (zinc sulfide, ZnS). The sulfur is recovered from these metal ores by roasting them—heating them strongly in air, which converts the sulfur to sulfur dioxide. For example,
Then the sulfur dioxide can go directly into the manufacture sulfuric acid , which is where more than 90% of the world's mined sulfur winds up.
Compounds of sulfur
Some sulfur is used directly as a fungicide and insecticide, in matches, fireworks, and gunpowder, and in the vulcanization of natural rubber. Most, however, is converted into a multitude of useful compounds.
Sulfur is in group 16 of the periodic table , directly below oxygen . It can form compounds in any one of its three major oxidation states: -2, +4 or +6.
Sulfuric acid is the parent acid of all sulfate compounds. Among the most important sulfates is calcium sulfate (CaSO4), which occurs naturally as gypsum, alabaster and selenite. Copper sulfate is used as an agricultural insecticide and to kill algae in water supplies. Alums are double sulfates of aluminum and another metal such as potassium, chromium or iron. The most common alum is potassium aluminum sulfate , KAl(SO4)2•12H2O. In water, it makes a gelatinous, goopy precipitate of aluminum hydroxide , Al(OH)3, which, when it sinks to the bottom, carries along with it all sorts of suspended dirt, leaving behind clear water. Alum is therefore used in water purification.
Hydrogen sulfide is the parent acid of the sulfides, a family of compounds that contain nothing but sulfur and a metal. This family includes many metal ores, including iron pyrites, galena, cinnabar, stibnite and zinc blende, as mentioned above, plus sulfides of copper and silver. Other sulfides are used in leather tanning, as pesticides , and in depilatories—creams that remove "unwanted hair" from the hides of cattle and from people.
Hydrogen sulfide itself is a foul-smelling gas. When eggs and certain other animal matter go rotten and putrefy, the stench is mostly hydrogen sulfide. It is often present in flatus—expelled intestinal gas. Hydrogen sulfide is extremely poisonous, but fortunately, it smells so bad that people don't hang around long enough to be overcome by it. Other very bad-smelling compounds of sulfur are the mercaptans, a family of organic sulfur-containing compounds. A mercaptan is the major ingredient in the aroma of skunks . A tiny amount of a gaseous mercaptan is deliberately added to the natural gas that is used for home heating and cooking, so that dangerous gas leaks can be detected by smell. Natural gas itself is odorless.
Emsley, John. Nature's Building Blocks: An A-Z Guide to theElements. Oxford: Oxford University Press, 2002.
Greenwood, N.N., and A. Earnshaw. Chemistry of the Elements. 2nd ed. Oxford: Butterworth-Heinemann Press, 1997.
Hancock P.L., and B.J. Skinner, eds. The Oxford Companion to the Earth. Oxford: Oxford University Press, 2000.
Kirk-Othmer Encyclopedia of Chemical Technology. 4th ed. New York: John Wiley & Sons, 1998.
Lide, D.R., ed. CRC Handbook of Chemistry and Physics. Boca Raton: CRC Press, 2001.
Robert L. Wolke
sulfur or sulphur (sŭl´fər), nonmetallic chemical element; symbol S; at. no. 16; interval in which at. wt. ranges 32.059–32.076; m.p. 112.8°C (rhombic), 119.0°C (monoclinic), about 120°C (amorphous); b.p. 444.674°C; sp. gr. at 20°C, 2.07 (rhombic), 1.957 (monoclinic), 1.92 (amorphous); valence -2, +4, or +6. Sulfur was known to the ancients; it is the brimstone of the Bible. It was first recognized as an element in 1777 by A. L. Lavoisier.
Properties and Compounds
Sulfur is found in Group 16 of the periodic table. It exhibits allotropy. Solid sulfur occurs principally in three forms, all of which are brittle, yellow in color, odorless, tasteless, and insoluble in water. Two of these solid forms are crystalline, composed of molecules containing eight sulfur atoms and having molecular weight 256.512 amu. Rhombic sulfur has orthorhombic crystalline structure and is stable below 95.5°C; most sulfur is in this form. The monoclinic, or prismatic, form has long, needlelike, nearly transparent crystals; it is stable between 95.5°C and its melting point but reverts to the rhombic form on standing at room temperature. Amorphous sulfur is a dark, noncrystalline, gumlike substance. It is often thought to be a supercooled liquid; it is formed by rapidly cooling molten sulfur, e.g., by pouring it into cold water. It slowly reverts to the rhombic form on standing. The crystalline forms are readily soluble in carbon disulfide, but the amorphous form is not. Many other forms of sulfur exist. Liquid sulfur is unusual in that its viscosity increases as it is heated. This property is thought to be due to the formation of long polymeric chains of sulfur molecules.
Sulfur is a chemically active element and forms many compounds, both by itself (sulfides) and in combination with other elements. It is part of many organic compounds, e.g., mercaptans (thiols) and thio compounds. It burns in air with a blue flame, forming sulfur dioxide, SO2.
Natural Occurrence and Processing
Sulfur is widely distributed in nature. It is found in many minerals and ores, e.g., iron pyrites, galena, cinnabar, zinc blende, gypsum, barite, and epsom salts and in mineral springs and other waters. It is found uncombined in some volcanic regions and in large underground deposits in Sicily and in Texas and Louisiana. Sulfur often occurs with coal, petroleum, and natural gas. Sulfur is found in meteorities, and deposits of it may be present near the lunar crater Aristarchus. The distinctive colors of Jupiter's moon Io are believed to result from forms of molten, solid, and gaseous sulfur. Sulfur is a component of all living cells. The amino acids cysteine, methionine, homocysteine, and taurine contain sulfur as do some common enzymes; it is a component of most proteins. Some forms of bacteria use hydrogen sulfide (H2S) in place of water in a rudimentary photosynthesislike process. Sulfur is absorbed by plants from soil as sulfate ions.
Sulfur is produced chiefly by the Frasch process, although it is also produced by the Sicilian method and by other methods. In the Sicilian method the sulfur-bearing ores are piled in a mound and ignited. The heat produced by the burning melts some of the sulfur, which is collected and cast. This sulfur is impure and is usually purified by sublimation. Sulfur is also recovered from natural gas, coal, crude oil, and other sources, e.g., the flue dusts and gases from the refining of metal sulfide ores. Elemental sulfur is obtained in several forms, including flowers of sulfur, a fine crystalline powder, and roll sulfur (cast cakes or sticks).
Elemental sulfur is used in black gunpowder, matches, and fireworks; in the vulcanization of rubber; as a fungicide, insecticide, and fumigant; in the manufacture of phosphate fertilizers; and in the treatment of certain skin diseases. The principal use of sulfur, however, is in the preparation of its compounds. The most important sulfur compound is sulfuric acid. Other important compounds include sulfur dioxide, used as a bleaching agent, disinfectant, and refrigerant; sodium bisulfite, used in paper manufacture; carbon disulfide, an important organic solvent; hydrogen sulfide, sulfur trioxide, and thionyl chloride, used as reagents in chemistry; Epsom salts (magnesium sulfate), used as a laxative, bath additive, exfoliant, and magnesium supplement in plant nutrition; the numerous other sulfate compounds; and sulfa drugs.
Sulfur has been known since prehistoric times. Because it is flammable, alchemists regarded sulfur as essential to combustion . The chemical properties of sulfur and its compounds, including the reaction of sulfur with mercury (Hg) to form a red solid, mercuric sulfide (HgS), and the use of sulfuric acid (H2SO4) as a solvent of metals , were discovered at about c.e. 250–300. Gunpowder, a mixture of sulfur, charcoal, and potassium nitrate (KNO3), was first used for military purposes in China in c.e. 904.
Sulfur is a tasteless, odorless, nonmetallic element. Sulfur along with selenium (Se) and tellurium (Te) are called chalcogens. The valences of sulfur are 2, 4, and 6, which can be represented by compounds such as hydrogen sulfide (H2S), sulfur dioxide (SO2), and barium sulfate (BaSO4), respectively. Pure sulfur is insoluble in water. The most stable variety of sulfur, rhombic sulfur, is a yellow crystalline solid.
In Earth's crustal composition, sulfur ranks thirteenth in abundance, with an estimated concentration of 0.05 percent. Sulfur exists in elemental form, as metallic sulfides, as sulfates, and, when combined with carbon and nitrogen, in organic forms. Most of the world's sulfur resource is located in North America. It is distributed, in descending order according to share of that resource, as follows: the United States and Canada have 26 percent and 22 percent, respectively, followed by Russia (11%), Saudi Arabia (5%), Japan (5%), Poland (4%), Germany (4%), and France (2%); the remaining 21 percent is distributed in other countries.
Sulfur is commercially important in the manufacture of chemicals such as sulfuric acid. The chemicals, in turn, are used in the manufacture of sulfa drugs, vulcanized rubber , acid batteries, dyes, and so on. In agriculture, sulfur is the fourth most important crop nutritive element, after nitrogen, phosphorus, and potassium. Its use in fertilizers is increasing rapidly. Sulfur is also used to manufacture poultry feed additives, pesticides, and parasiticides.
see also Chalcogens.
Hampel, Clifford A., and Hawley, Gessner G. (1976). Glossary of Chemical Terms. New York: Van Nostrand Reinhold.
Tisdale, Samuel L.; Nelson, Werner L.; and Beaton, James D. (1985). Soil Fertility and Fertilizers, 4th edition. New York: Macmillan.
sul·fur / ˈsəlfər/ (also chiefly Brit. sulphur) • n. 1. the chemical element of atomic number 16, a yellow combustible nonmetal. It occurs uncombined in volcanic and sedimentary deposits, as well as being a constituent of many minerals and petroleum. It is normally a bright yellow crystalline solid, but several other allotropic forms can be made. (Symbol: S) ∎ the material of which hellfire and lightning were believed to consist. ∎ a pale greenish-yellow color: [as adj.] the bird's sulfur-yellow throat. 2. an American butterfly (Colias, Phoebis, and other genera, family Pieridae) with predominantly yellow wings that may bear darker patches. • v. [tr.] disinfect or fumigate with sulfur. DERIVATIVES: sul·fur·y adj.