(also spelled Sulphur)
is a solid, nonmetallic element. It is one of the elements that are essential to plants and animals. In the human body, sulfur aids in the development of the bones. It also helps the blood to clot and the muscle cells to change food into energy and new tissue. Foods that are rich in sulfur include eggs, cabbage, horseradish, and onion.
Sulfur has been known since ancient times. It was isolated as an element by Antoine-Laurent Lavoisier, sometime around 1777. The word sulfur is from the Latin word sulphurium, which means "brimstone."
Properties
Sulfur has an atomic number of 16 and an atomic weight of 32.064.
Sulfur is brittle and has almost no taste. When it is rubbed or melted, it gives off a "rotten egg" odor. It does not dissolve in water but dissolves readily in carbon dioxide.
Sulfur comes in three forms -- rhombic crystals, which have three unequal axes, each of which is at right angles to the other; monoclinic crystals, which are very transparent and shaped like prisms; and, amorphous, which may be formed by dropping molten sulfur into cold water, redily changes to the crystalline, rhombic form. Ordinary lump sulfur occurs in rhombic or monoclinic crystals, and is pale yellow in color.
Rhombic sulfur melts at 112.8º C (235º F.) and monoclinic melts at 119.0º C (246.2º F.). When heated above its melting point, sulfur becomes syrupy or a solid. Above 250º C, the sulfur changes back into a liquid. The boiling point of sulfur is 444.6º C (832º F.). When it boils it gives off a yellowish-brown vapor which condenses into fine yellow grains of powder known as flowers of sulfur. The roll sulfur that is used commercially is made by pouring liquid sulfur into cylinder-shaped molds to harden.
Sulfur burns in air with a pale-blue flame and gives off sulfur dioxide, a colorless gas. When sulfur dioxide is exposed to moist air, it mixes with the moisture in the air and forms sulfurous acid, a major component of acid rain.
Sources
Large quantities of sulfur are found in the earth's crust, both in a pure state and in combination with other substances. Sulfur occurs in a pure state in volcanic regions. It combines with metals to form such valuable metal ores as cinnabar, galena, sphalerite, and stibnite. Gypsum, also called calcium sulfate, is an important mineral that contains sulfur.
The United States produces much of the world's sulfur. Spain, Mexico, Japan, and Italy are also major supplies of sulfur.
The most common method of mining sulfur is called the superheated water method. Water is superheated under increased pressure so that its boiling point rises above sulfur's melting point. Four pipes, one inside the other, bore into the sulfur deposit. The two outside pipes force the hot water into the sulfur, causing the sulfur to melt. The fourth pipe sends down compressed air into the deposit, causing the melted sulfur to form a froth, which is forced up the third pipe. Sulfur of about 99 per cent purity is obtained in this way. The frothy sulfur is sprayed into bins and allowed to dry thoroughly in the open air.
Sulfur may be recovered in acid form from gases at metallic sulfide smelters. Sulfur as an element may be obtained from some natural gases and from refinery gases.
Uses
Pure sulfur is used to make up a group of substances known as sulfur compounds -- sulfuric acid, the sulfite salts, sulfur dioxide, etc. Sulfur dioxide is used as a bleaching agent, solvent, disinfectant, and as a refrigerant. Sulfur mixes with saltpeter and charcoal to form gunpowder, and is used to some extent in the manufacture of matches. On farms, sulfur is used in the manufacture of fertilizers, and in preparations that destroy insects and plant pests. Sulfur also has an important use in the making of paper pulp, which is produced by the action of calcium bisulfite on wood cellulose. Sulfur is used in various medicines and is considered helpful in certain skin diseases. Photographers use sodium thisulfate to fix photographic images after development.
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