_Tin_ is about the only metal of industrial value whose ores are not found in paying quantities in the United States. Small quantities occur in San Bernardino County, Cal., and in the vicinity of Bering Strait, Alaska, but it is doubtful if either will ever pay for development. About three-fifths of the world's product comes from the Straits Settlements on the Malay Peninsula; the nearby islands of Banca and Billiton also yield a considerable quantity. The mines of Cornwall, England, have been worked for two thousand years and were probably the source of the tin that made the "bronze age." The United States imports yearly about twenty million dollars worth of tin, about half of which comes from the Straits Settlements. This is used almost wholly for the manufacture of tin plate[48]--that is, sheet-iron coated with tin. Much of the block tin imported from Great Britain is returned there in the form of tin plate, being manufactured in the United States much more economically than in Europe. _Nickel_ occurs in New Caledonia, in Canada, and in the State of Missouri. It is used in the manufacture of small coins and for plating iron and steel. It is an essential in the metal known as "nickel steel" which is now generally used in armor-plate and propeller-shafts, about four per cent. of nickel being added to the steel. Most of the product used in the United States is imported from Canada. _Manganese_, a metal resembling iron, occurs in Russia, Brazil, and Cuba, Russia producing about half the total output. It is used mainly to give hardness to steel. The propeller-blades of large steamships are usually made of manganese bronze. The building of war-ships in the United States during the past few years has led to the extensive use of manganese for armor-plate, and manganese ores to the amount of more than two hundred and fifty thousand tons were imported in 1900. More than one-half of this came from Russia; most of the remaining half from Brazil. _Zinc_ is abundant in nearly every part of the world. In the United States the best known mines are in the Galena-Joplin District, in Missouri and Kansas, which produce about two-thirds of the home product--mainly from the ore _blende_, a sulphide. There are also extensive zinc-mining operations in Illinois, New Jersey, and Pennsylvania. The lower Rhine District, Great Britain, and Silesia are the chief European sources. Sheet-zinc is found in nearly every dwelling in the United States, and zinc-coated or "galvanized" iron has become a domestic necessity. Zinc-white is extensively used as a pigment. About two hundred and fifty million pounds of crude zinc, or "spelter," are produced in the United States; forty-five million pounds were exported in 1900, mainly to Great Britain. QUESTIONS FOR DISCUSSION What are the qualities that make iron the most valuable of metals? In what ways does commerce depend on iron and steel?