to produce acidity.

_Sulphuret_, a combination of sulphur with a base.

[Footnote 8: See Chapter XIII., article Oxygen.]

What are the uses of Copper?

They are too various to be enumerated. In sheets it is much used to
sheathe the bottoms of ships, for boilers, and other utensils. Copper
coin was the only money used by the Romans till the 485th year of
their city, when silver began to be coined. In Sweden, houses are
covered with this metal.

What is a Mine?

A cavity under ground, formed for the purpose of obtaining metals,
&c.; mines are often very deep and extensive. The descent into them is
by a pit, called a shaft; the clues by which mines are discovered,
are, mineral springs, the discoloration of vegetables, the appearance
of pieces of ore, &c.

_Clues_, signs or means by which things hidden are brought
to light.

What is Brass?

A factitious metal, consisting of copper and zinc. Brass is lighter
and harder than pure copper, and less subject to rust; owing to these
properties, together with its beautiful color, it is extremely useful
in the manufacture of many utensils.

_Factitious_, made by art, not found in a natural state.

What is Zinc?

A metal of a brilliant bluish white color. Its name was unknown to the
ancient Greeks and Arabians. It is mixed with other substances in the
ore, from which it is obtained by smelting in the furnace. It has
never yet been found native or pure.

For what is Zinc used?

From its readiness to dissolve in all acids, and unite with other
metals, it is used in alloy with them in the composition of brass, &c.
Thin sheets of zinc are also used to cover roofs of houses, and in the
manufacture of various household utensils.

What is Lapis Calaminaris?

Lapis Calaminaris, or calamine stone, is a native carbonate of zinc,
of some use in medicine, but chiefly in founding. It is, sometimes
brownish, as that found in Germany and England, or red, as that of
France. It is dug out of mines, usually in small pieces; generally out
of those of lead. Calamine is mostly found in barren, rocky soils.

_Founding_, the art of casting metals.

CHAPTER XI.

YAMS, MANGOES, BREAD-FRUIT, SHEA OR BUTTER TREE, COW TREE, WATER
TREE, LICORICE, MANNA, OPIUM, TOBACCO, AND GUM.

What are Yams?

The roots of a climbing plant growing in tropical climates. The root
of the yam is wholesome and well-flavored; nearly as large as a man's
leg, and o