forming the
metal into a wire, and hanging on weights, to find how much will be
required to break it. If we have two wires, the first with a transverse
area only one-quarter that of the second, and the first breaks at 25
pounds, while the second breaks at 50 pounds, the tenacity of the first
is twice as great as that of the second.

To the boy who understands simple ratio in mathematics, the problem
would be like this:

25 x 4 : 50 x 1, or as 2 : 1.

THE MOST TENACIOUS METAL.--Steel has the greatest tenacity of all
metals, and lead the least. In proportion to weight, however, there are
many substances which have this property in a higher degree. Cotton
fibers will support millions of times their own weight.

There is one peculiar thing, that tenacity varies with the form of the
body. A solid cylindrical body has a greater strength than a square one
of the same size; and a hollow cylinder more tenacity than a solid one.
This principle is well known in the bones of animals, in the feathers of
birds, and in the stems of many plants.

In almost every metal tenacity diminishes as the temperature increases.

DUCTILITY.--This is a property whereby a metal may be drawn out to form
a wire. Some metals, like cast iron, have absolutely no ductility. The
metal which possesses this property to the highest degree, is platinum.
Wires of this metal have been drawn out so fine that over 30,000 of them
laid side by side would measure only one inch across, and a mile of such
wire would weigh only a grain, or one seven-thousandth of a pound.

MALLEABILITY.--This is considered a modification of ductility. Any
metal which can be beaten out, as with a hammer, or flattened into
sheets with rollers, is considered malleable. Gold possesses this
property to the highest degree. It has been beaten into leaves one
three-hundred-thousandth of an inch thick.

HARDNESS.--This is the resistance which bodies offer to being scratched
by others. As an example, the diamond has the capacity to scratch all,
but cannot be scratched by any other.

ALLOYS.--Alloys, that is a combination of two or more metals, are harder
than the pure metals, and for this reason jewelry, and coins, are
usually alloyed.

The resistance of a body to compression does not depend upon its
hardness. Strike a diamond with a hammer and it flies to pieces, but
wood does not. One is brittle and the other is tough.

The machinist can utilize this property by understanding that