vered. These oxides often give a
characteristic color to the clear borax glass, and borax beads are
therefore often used in testing for the presence of metals, instead of
the metaphosphoric acid bead already described.

The reason that metallic oxides dissolve in borax is that borax
contains an excess of acid anhydride, as can be more easily
seen if its formula is written 2NaBO_{2} + B_{2}O_{3}. The
metallic oxide combines with this excess of acid anhydride,
forming a mixed salt of metaboric acid.

Borax is extensively used as a constituent of enamels and glazes for
both metal ware and pottery. It is also used as a flux in soldering and
brazing, and in domestic ways it serves as a mild alkali, as a
preservative for meats, and in a great variety of less important
applications.

EXERCISES

1. Account for the fact that a solution of borax in water is alkaline.

2. What weight of water of crystallization does 1 kg. of borax contain?

3. When a concentrated solution of borax acts on silver nitrate a borate
of silver is formed. If the solution of borax is dilute, however, an
hydroxide of silver forms. Account for this difference in behavior.

CHAPTER XXII

THE METALS

~The metals.~ The elements which remain to be considered are known
collectively as the metals. They are also called the base-forming
elements, since their hydroxides are bases. A metal may therefore be
defined as an element whose hydroxide is a base. When a base dissolves
in water the hydroxyl groups form the anions, while the metallic element
forms the cations. From this standpoint a metal can be defined as an
element capable of forming simple cations in solution.

The distinction between a metal and a non-metal is not a very sharp one,
since the hydroxides of a number of elements act as bases under some
conditions and as acids under others. We have seen that antimony is an
element of this kind.

~Occurrence of metals in nature.~ A few of the metals are found in nature
in the free state. Among these are gold, platinum, and frequently
copper. They are usually found combined with other elements in the form
of oxides or salts of various acids. Silicates, carbonates, sulphides,
and sulphates are the most abundant salts. All inorganic substances
occurring in nature, whether they contain a metal or not, are called
_minerals_. Those minerals from which a useful substance can be
extracted are called _ores_ of the substan