ny of its chemical properties; for instance it burns
very readily in oxygen, and consequently native silicon is unknown--it
is always found in combination with one or more other elements.
When it bums, each atom of silicon unites with two atoms of oxygen
to form a compound known to chemists as silica (SiO2), and to the
small boy as "sand" and "agate."

Iron ore (an oxide of iron) contains more or less sand and dirt
mixed in it when it is mined, and not only the iron oxide but also
some of the silicon oxide is robbed of its oxygen by the smelting
process. Pig iron--the product of the blast furnace--therefore
contains from 1 to 3 per cent of silicon, and some silicon remains
in the metal after it has been purified and converted into steel.

However, silicon, as noted above, burns very readily in oxygen,
and this property is of good use in steel making. At the end of
the steel-making process the metal contains more or less oxygen,
which must be removed. This is sometimes done (especially in the
so-called acid process) by adding a small amount of silicon to
the hot metal just before it leaves the furnace, and stirring it
in. It thereupon abstracts oxygen from the metal wherever it finds
it, changing to silica (SiO2) which rises and floats on the surface
of the cleaned metal. Most of the silicon remaining in the metal
is an excess over that which is required to remove the dangerous
oxygen, and the final analysis of many steels show enough silicon
(from 0.20 to 0.40) to make sure that this step in the manufacture
has been properly done.

MANGANESE is a metal much like iron. Its chemical symbol is Mn. It
is somewhat more active than iron in many chemical changes--notably
it has what is apparently a stronger attraction for oxygen and
sulphur than has iron. Therefore the metal is used (especially in
the so-called basic process) to free the molten steel of oxygen,
acting in a manner similar to silicon, as explained above. The
compound of manganese and oxygen is readily eliminated from the
metal. Sufficient excess of elemental manganese should remain so
that the purchaser may be sure that the iron has been properly
"deoxidized," and to render harmless the traces of sulphur present.
No damage is done by the presence of a little manganese in steel,
quite the reverse. Consequently it is common to find steels containing
from 0.3 to 1.5 per cent.

ALLOYING ELEMENTS.--Commercial steels of even the simplest types
are therefore prim