Brittle, pale-yellow, non-metallic element, atomic number 16, relative atomic mass 32.064. It occurs in three allotropic forms: two crystalline (called rhombic and monoclinic, following the arrangements of the atoms within the crystals) and one amorphous. It burns in air with a blue flame and a stifling odour. Insoluble in water but soluble in carbon disulphide, it is a good electrical insulator. Sulphur is widely used in the manufacture of sulphuric acid (used to treat phosphate rock to make fertilizers) and in making paper, matches, gunpowder and fireworks, in vulcanizing rubber, and in medicines and insecticides.
It is found abundantly in nature in volcanic regions combined with both metals and non-metals, and also in its elemental form as a crystalline solid. It is a minor constituent of proteins, and has been known since ancient times.
Between 20 and 50 million tonnes of sulphur are returned from the oceans to the atmosphere every year in the form of dimethyl sulphide (DMS), the gas that gives sea air its bracing smell. DMS is a breakdown product of a salt produced by marine algae to maintain their osmotic balance (see osmosis). Human activity releases about 80 million tonnes of sulphur. The presence of sulphur in fossil fuels can lead to emissions of sulphur dioxide, which has been blamed for the extensive damage to forests across central and eastern Europe in the second half of the 20th century.
On the other hand, sulphur is an essential plant nutrient and, according to German research in 1995, reductions in European sulphur emissions have resulted in an increase in sulphur deficiency diseases in crops and other plants, in particular members of the Brassica family, especially oilseed rape.
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