Charles Perkins, age 13, of Hutchinson, Kan., for his question:
HOW IS TIN PROCESSED?
Tin is a soft, white metal that was one of the first elements known to man. Although some tin is found naturally, most of the world's supply comes from the extraction of the metal from its principal ore, cassiterite, composed of tin dioxide.
Cassiterite occurs and is mined in two forms: primary deposits, which occur as veins or lodes; and secondary, alluvial or placer deposits, which are left by water.
After the ore is mined, it is crushed and the lighter particles of sand and clay are washed away. The heavier particles of cassiterite remain. The purer the ore that is put into a smelter, the purer the final product will be.
The cleaned ore is mixed with coke and limestone or sand and heated in a blast furnace. From the bottom of the blast furnace a crude metallic tin is separated. This crude tin is then refined by either the fire refining process or the electrical refining process.
In the fire refining process, the tin is melted in large kettles into which poles of green wood are placed. The green wood produces gases that cause a violent boiling, bringing the metal to the surface where the oxygen in the air can act on its impurities. The film of oxides that forms is removed by skimming, and relatively pure tin remains.
In the electrical refining process, the metal is dissolved and deposited as pure tin by an electric current.
Some tin is recovered through the processing of old tin cans and other scraps of tin.
Tin is resistant to corrosion and for this reason it is used to protect other metals from the action of the air. The so called tin can is made of a sheet of iron with a thin coating of tin on each side. The tin prevents rusting of the iron. Tin also resists weak acids, making the cans ideal as containers for food.
Almost 90 percent of the tin plate produced in the United States is used in the manufacture of tin cans.
Lots of tin is mixed with copper to form bronze, an important alloy.
Mixed with lead, tin forms solder, which is used in joining other metals. The lead tin alloy is rolled out to form tin foil, a thin metal sheet used for wrapping some food products and for making collapsible containers for such materials as toothpaste.
The compound of tin and chlorine, tin chloride, is used in the textile industry for printing calico and for weighing silk.
Tin was used as early as 1000 B.C. by the Phoenicians. These people sailed through the Strait of Gibraltar to islands, probably the southern part of England, that they called the Cassiterides, or Tin Islands. It was their word that furnished the name for the important !in ore, cassiterite.