361Sulfur............................................
Sulfur or sulphur (British English; is a chemical element with symbol S and atomic
number 16. It is an abundant, multivalent non-metal. Under normal conditions, sulfur
atoms form cyclic octatomic molecules with chemical formula S 8. Elemental sulfur is a
bright yellow crystalline solid when at room temperature. Chemically, sulfur can react as
either an oxidant or reducing agent. It oxidizes most metals and several nonmetals,
including carbon, which leads to its negative charge in most organosulfur compounds, but
it reduces several strong oxidants, such as oxygen and fluorine.
Sulfur occurs naturally as the pure element (native sulfur)
and as sulfide and sulfate minerals. Elemental sulfur
crystals are commonly sought after by mineral collectors for
their brightly colored polyhedron shapes. Being abundant in
native form, sulfur was known in ancient times, mentioned
for its uses in ancient Greece, China and Egypt. Fumes
from burning sulfur were used as fumigants, and sulfur-
containing medicinal mixtures were used as balms and
antiparasitics.
Sulfur is referenced in the Bible as brimstone (burn stone)
in English, with this name still used in several nonscientific
tomes. It was needed to make the best quality of black
gunpowder. In 1777, Antoine Lavoisier helped convince the scientific community that
sulfur was a basic element, rather than a compound.
Elemental sulfur was once extracted from salt domes where it sometimes occurs in nearly
pure form, but this method has been obsolete since the late 20th century. Today, almost
all elemental sulfur is produced as a byproduct of removing sulfur-containing contaminants
from natural gas and petroleum. The element's commercial uses are primarily in fertilizers,
because of the relatively high requirement of plants for it, and in the manufacture of sulfuric
acid, a primary industrial chemical.
Other well-known uses for the element are in matches, insecticides and fungicides. Many
sulfur compounds are odiferous, and the smell of odorized natural gas, skunk scent,
grapefruit, and garlic is due to sulfur compounds. Hydrogen sulfide produced by living
organisms imparts the characteristic odor to rotting eggs and other biological processes.
Sulfur is an essential element for all life, and is widely used in biochemical processes. In
metabolic reactions, sulfur compounds serve as both fuels and respiratory (oxygen-
alternative) materials for simple organisms.
Sulfur in organic form is present in the vitamins biotin and thiamine, the latter being named
for the Greek word for sulfur. Sulfur is an important part of many enzymes and in
antioxidant molecules like glutathione and thioredoxin. Organically bonded sulfur is a
component of all proteins, as the amino acids cysteine and methionine.
Disulfide bonds are largely responsible for the mechanical strength and insolubility of the
protein keratin, found in outer skin, hair, and feathers, and the element contributes to their
pungent odor when burned.