Sulfur, chemical symbol S, has beeen known since antiquity, and its occurrence in the natural state in Sicily insured its availability to the early Mediterranean civilizations. Homer mentioned its medicinal properties about 900 BC, and the fumes of burning sulfur (sulfur dioxide, SO2) have long been used for bleaching textiles and for fumigation.
The name can be traced to the Sanskrit word sulveni which was the basis of the Roman word sulphurium. It is also known as brimstone from the German word Brennstein meaning burning stone. To the alchemist sulfur, along with mercury, was an essential ingredient of all metals, and it was not until the work of the French chemist Antoine Laurent Lavoisier in the late eighteenth century that it was classified as a chemical element.
In the PERIODIC TABLE (a table of the elements arranged according to their atomic weights) sulfur is situated toward the end of the third period. Accordingly it is a nonmetal and a good thermal and electric insulator. At room temperature it is a yellow crystalline solid, tasteless and odorless. There are two common crystalline forms or allotropes — the more stable of these, known as alpha (a) sulfur, has an orthorhombic CRYSTAL structure and melts at 235° F (113° C). Above 203° F (95° C), however, the other crystalline form designated beta (13) sulfur is the more stable — it has a monoclinic crystal structure and melts at 246° F (119° C). The transition between the two forms takes place at a fairly leisurely pace, so that a-sulfur heated rapidly will melt before any (3-sulfur has time to form. Similarly, if the beta form is crystallized from the melt, or if a-sulfur is held between 203° F (95° C) and 235° F (113° C) and then cooled rapidly to room temperature, the monoclinic crystals of (3-sulfur will be preserved in a metastable (apparently stable) condition, although they will revert to the alpha form over a period of a day or so. Crystals of the alpha form can, however, be prepared directly by crystallization from a solution of sulfur in carbon disulfide, CS2.
Plastic sulfur is made by pouring liquid sulfur at nearly its boiling point into cold water. It is noncrystalline, being a supercooled form of the viscous melt, and it reverts to the crystalline alpha form on standing. Other types of noncrystalline sulfur, known generally as amorphous sulfur, can be formed by the action of light on solutions of sulfur in carbon disulfide or by various reactions which precipitate sulfur from solutions of its compounds. Flowers of sulfur, prepared by SUBLIMATION, contain some of the amorphous form which can be separated by dissolving out the crystalline component.
The occurrence of native sulfur (free sulfur rather than a sulfur-containing compound) is associated with regions of volcanic activity. The deposits in Sicily contain about 20 per cent sulfur which is extracted by burning the rock with a limited supply of air in kilns. The fraction of the sulfur burned provides heat to melt out the remainder – it is cheaper to use sulfur itself as fuel than to import coal or oil.