f 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?

What substances are used for food, clothing, or domestic purposes that
are not manufactured by the aid of iron?

Ingot or billet steel is rated at about one cent per pound; the
hair-springs of watches are worth several thousand dollars per pound;
what makes the difference in their value?

What are the qualities tha