Tin, a chemical element that exists in two forms, one metallic and the other nonmetallic. The metallic form, known as white tin, or beta tin, is the most familiar form. White tin is silvery white and somewhat harder than lead but not as hard as copper. It is corrosion-resistant and malleable (capable of being hammered or rolled into thin sheets), and can combine with most other metals to form alloys. Gray tin, or alpha tin, is a gray powder. It is chemically stable only at low temperatures. White tin of high purity continually exposed to temperatures of 32 F. (0 C.) or lower may slowly change into gray tin.

Tin was one of the first metals known to humans. It was used in ancient Mesopotamia and Syria as early as 3000 B.C. in bronze, an alloy of tin and copper used for making tools and weapons.

Tin is usually found combined with oxygen in the ore cassiterite, or tinstone. The metal is obtained by smelting the ore with coke. About one-fourth of the world's tin is mined in China. Other leading producers have included Indonesia, Brazil, Bolivia, Malaysia, and Peru. Production often varies as low tin prices cause some mines to close.

Uses of Tin

Only white tin is commercially important. It is widely used in the form of tinplatethin sheets of steel or iron coated with tin to protect them from rust and other types of corrosion. Most tinplate is made by an electrolytic process known as electroplating. The most important use of tinplate is for making tin cans. Such cans, made of steel sheets coated with tin, are excellent containers for food because tin is highly resistant to the weak acids present in some foods. Tin is also used as a protective coating for copper wire and lead pipes.

Tin is rolled into thin sheets that can be made into collapsible tubes, such as those used for adhesives and artists' paints. Tinfoil is a thin sheeting of tin or of tin alloyed with antimony or lead (or both). It is used as a moisture-proof wrapping for tobacco and various food products.

A large percentage of the tin produced is used in solders, bronzes, and other alloys.

Tin also forms many useful chemical compounds. Their names are based on the Latin word for tin, stannum. Stannous chloride is used in the manufacture of synthetic dyes and other chemicals. Stannous fluoride is used in toothpaste. Several tin compounds, such as stannic chloride and stannous oxide, are used as mordants (substances that cause fabrics to accept dyes readily). Stannic oxide produces the glaze of certain ceramics. It is also an important polishing agent for marble and other decorative stones. Many organic tin compounds are used to prevent the decomposition of certain chemicals in plastics, wood preservatives, and fungicides.

Symbol: Sn (from the Latin). Atomic number: 50. Atomic weight: 118.71. Specific gravity (white tin): 7.3. Hardness (white tin): 1.8. Melting point (white tin): 449.4 F. (231.9 C.). Boiling point (white tin): 4,118 F. (2,270 C.). Tin has 10 stable isotopes: Sn-112, Sn-114 through Sn-120, Sn-122, and Sn-124. It belongs to Group IVA of the Periodic Table and can have a valence of +2 or +4.