mainly found on Earth as sulfates in rocks or as free sulfur. The largest
deposits of sulfur in the United States are in Louisiana and Texas. Sulfur
also occurs in combination with several metals such as lead and mercury,
as PbS and HgS. Sulfur appears as the yellow aspects of soil in many regions.
mined early in the form of the yellow element and used for gunpowder and
fireworks. While bacteria digest plant matter, they emit H2S,
hydrogen sulfide, a gas that has the "rotten egg" smell characteristic
of swamps and sewage. Sulfur is an essential element of biological molecules
in small quantities.
its compounds are important elements of industrial processes. Sulfur dioxide
(SO2) is a bleaching agent and is used to bleach wood pulp for paper and
fiber for various textiles such as wool, silk, or linen. SO2 is a colorless
gas that creates a choking sensation when breathed. It kills molds and
bacteria. It is also used to preserve dry fruits, like apples, apricots,
and figs, and to clean out vats used for preparing fermented foods such
as cheese and wine.
acid, H2SO4, is a very widely used chemical. Over
30 million tonnes of sulfuric acid are produced every year in the U.S.
alone. The acid has a very strong affinity for water. It absorbs water
and is used in various industrial processes as a dehydrating agent. The
acid in the automobile battery is H2SO4. It is used
for "pickling" steel, that is, to remove the oxide coating from
the steel surface before it is coated with tin or electroplated with zinc.
is also a biologically important atom. Although only small amounts of
sulfur are necessary for biological systems, disulfide bridges form a
critical function in giving biological important molecules specific shapes
and properties. (See Biological Systems.)
released into the atmosphere through the burning of fossil fuels --especially
high sulfur coal--and is a primary constituent of acid rain. Sulfuric
acid (H2SO4) is the primary constituent of acid
rain (see Atmospheric System)
in about all regions other than California. Sulfur dioxide and carbonyl
sulfide (COS) occur in small quantities in the atmosphere; but due to
its high reactivity, sulfur is quickly deposited as compound (sulfates)
on land and other surfaces.
S1: The Sulfur Cycle.
S1 shows the biogeochemical cycle of sulfur. As in the case of nitrogen,
the figure shows the large quantities. Local activities such as coal burning
can release large amounts in a small area. Sulfur compounds can also be
transported from the higher altitudes from tall "smoke stacks"
and contribute to acid rain far from the sources.