on of the ground, in mechanical arts or trades, in
architecture or navigation; it is therefore of the greatest use to
man. Iron tools have been used in all European countries as long as
their histories have existed; this metal appears likewise to have been
known and used by the inhabitants of the world in the earliest ages,
being frequently mentioned in the Holy Scriptures. In the fourth
chapter of Genesis, Tubalcain is spoken of as "a hammerer and
artificer in every work of brass and iron," and thus their existence
was evidently known at that early period of the world.

_Artificer_, one who works or makes.

_Fusible_, capable of being melted by fire.

[Illustration: THE SALT MINES OF WIELICZCA.]

What do you mean by Metals?

Useful substances dug from the bowels of the earth, being sometimes
found pure, but mostly combined with other matter. They are
distinguished by their weight, tenacity, hardness, opacity, color, and
peculiar lustre, known as the metallic lustre; they are fusible by
heat, and good conductors of heat and electricity; many of them are
malleable, and some extremely ductile. Those which were first known
are gold, silver, iron, copper, mercury, lead, and tin.

_Tenacity_, the firmness with which one part adheres to
another.

_Opacity_, want of transparency or clearness.

What are Metals called in their natural state?

Ores; so named because the metal contained in them is either mixed
with other metals, or with mineral earths, from which they are
separated and purified by various means: such as washing, roasting,
&c., but the method is always regulated by the nature of the ore.

What is Copper?

A hard, heavy, ductile metal, found native, and in many ores; of these
the most important is _copper pyrites_, which is a sulphuret of
copper. Next to gold, silver, and platinum, copper is the most
malleable and ductile of metals; it may be drawn into wires as fine as
hair, or beaten into leaves as thin as those of silver. The rust of
copper is very poisonous. Copper, mixed with a certain quantity of
tin, forms bell-metal. With a smaller proportion, it forms bronze, a
substance used in sculpture for casting figures and statues. It is an
abundant metal, and is found in various parts of the world. Native
oxides of copper are found in Cornwall, Siberia, and in North and
South America.

_Oxide_, a substance combined with Oxygen,[8] in a
proportion not sufficient