Description
Sulfur is a chemical element with the symbol S and atomic number 16. It is a yellow nonmetal. As early as the 9th century BC, it was known that a mixture of sulfur, coal, and tar was extremely flammable, and therefore it was frequently used in warfare. In the 12th century, gunpowder, a mixture of potassium nitrate, charcoal, and sulfur, was invented in China. In mythology, sulfur was often associated with hell. Early alchemists used a symbol for sulfur consisting of a triangle with a cross on top. It was learned through experimentation that sulfur reacts easily with mercury. Around 1774, the scientist Antoine Lavoisier discovered that sulfur is a chemical element, not a compound. The name sulfur likely derives from the Indo-European *suel-, "to swell," "to boil." Sulfur is a nonmetal with a bright yellow color. As an independent element, it is odorless. When burned, it emits a blue light and forms pungent sulfur dioxide. It is insoluble in water, but readily dissolves in carbon disulfide. Sulfur chemistry is an important branch of chemistry, mineralogy, environmental science, and technology. The element itself forms a yellow crystalline solid with a rhombic crystal structure, consisting of a stack of ring-shaped S8 molecules. When powdered, the substance resembles wheat flour (also called sulfur flower) (except for its color). It is an insulator. At 112.8°C, sulfur transforms into a monoclinic phase, which then melts at 119.0°C. The liquid initially consists of S8 molecules and is then not very viscous. At higher temperatures, the viscosity increases dramatically because ring-opening and polymerization occur. When the polymer melt is quenched in cold water, plastic sulfur forms, an amorphous form that gradually crystallizes. Sulfur boils at 444.674°C. On Earth, sulfur occurs in large quantities as a compound in minerals such as pyrite, galena, sphalerite, gypsum, and barite. In volcanic regions, it is found in small quantities in its elemental form, often in solfataras. On other planets with active volcanism, sulfur is frequently found. Jupiter's moon Io is a clear example. However, the most important source of sulfur is the petrochemical industry, where sulfur-containing compounds are removed from gas and oil to create cleaner fuels. For example, hydrogen sulfide is removed from gas through amine gas treatment and then converted into elemental sulfur in the Claus process. Sulfur is present in all living things because the amino acids methionine and cysteine contain sulfur compounds. This means that most proteins cannot exist without sulfur. Since petroleum originated from organisms, the presence of non-elemental sulfur in it is not surprising.
