ce. These two terms are most
frequently used in connection with the metals.

~Extraction of metals,--metallurgy.~ The process of extracting a metal
from its ores is called the metallurgy of the metal. The metallurgy of
each metal presents peculiarities of its own, but there are several
methods of general application which are very frequently employed.

1. _Reduction of an oxide with carbon._ Many of the metals occur in
nature in the form of oxides. When these oxides are heated to a high
temperature with carbon the oxygen combines with it and the metal is set
free. Iron, for example, occurs largely in the form of the oxide
Fe_{2}O_{3}. When this is heated with carbon the reaction expressed in
the following equation takes place:

Fe_{2}O_{3} + 3 C = 2 Fe + 3 CO.

Many ores other than oxides may be changed into oxides which can then be
reduced by carbon. The conversion of such ores into oxides is generally
accomplished by heating, and this process is called _roasting_. Many
carbonates and hydroxides decompose directly into the oxide on heating.
Sulphides, on the other hand, must be heated in a current of air, the
oxygen of the air entering into the reaction. The following equations
will serve to illustrate these changes in the case of the ores of iron:

FeCO_{3} = FeO + CO_{2},

2Fe(OH)_{3} = Fe_{2}O_{3} + 3H_{2}O,

2FeS_{2} + 11O = Fe_{2}O_{3} + 4SO_{2}.

2. _Reduction of an oxide with aluminium._ Not all oxides, however, can
be reduced by carbon. In such cases aluminium may be used. Thus chromium
may be obtained in accordance with the following equation:

Cr_{2}O_{3} + 2 Al = 2 Cr + Al_{2}O_{3}.

This method is a comparatively new one, having been brought into use by
the German chemist Goldschmidt; hence it is sometimes called the
Goldschmidt method.

3. _Electrolysis._ In recent years increasing use is being made of the
electric current in the preparation of metals. In some cases the
separation of the metal from its compounds is accomplished by passing
the current through a solution of a suitable salt of the metal, the
metal usually being deposited upon the cathode. In other cases the
current is passed through a fused salt of the metal, the chloride being
best adapted to this purpose.

~Electro-chemical industries.~ Most of the electro-chemical industries of
the country are carried on where water power is abundant, since this
furnishes the cheapest means for the generation of electrical