olution becomes saturated with this substance through
evaporation, it separates in the form of crystals. In solution
this substance can give hydrogen ions, and therefore possesses
acid properties; it can also give the ions characteristic of a
salt. It is therefore called an _acid salt_.

DEFINITION: _An acid salt is one which can give the ions of an
acid and of a salt when in solution._

3. _Normal salts._ Salts which are the products of complete
neutralization, such as Na_{2}SO_{4}, and which in solution can
give neither hydrogen nor hydroxyl ions, but only the ions of a
salt, are called _normal salts_ to distinguish them from acid
and basic salts.

~Methods of expressing reactions between compounds in solution.~ Chemical
equations representing reactions between substances in solution may
represent the details of the reaction, or they may simply indicate the
final products formed. In the latter case the formation of ions is not
indicated. Thus, if we wish to call attention to the details of the
reaction between sodium hydroxide and hydrochloric acid in solution, the
equation is written as follows:

Na^{+}, OH^{-} + H^{+}, Cl^{-} = Na^{+}, Cl^{-} + H_{2}O.

On the other hand, if we wish simply to represent the final products
formed, the following is used.

NaOH + HCl = NaCl + H_{2}O.

Both of these methods will therefore be used:

~Radicals.~ It has been emphasized that the hydroxyl group (OH) always
forms the anion of a base, while the group NO_{3} forms the anion of
nitric acid and sodium nitrate; the group SO_{4}, the anion of sulphuric
acid and calcium sulphate. A group of elements which in this way
constitutes a part of a molecule, acting as a unit in a chemical change,
or forming ions in solution, is called a _radical_. Some of these
radicals have been given special names, the names signifying the
elements present in the radical. Thus we have the hydroxyl radical (OH)
and the nitrate radical (NO_{3}).

DEFINITION: _A radical is a group of elements forming part of a
molecule, and acting as a unit in chemical reactions._

~Names of acids, bases, and salts.~ Since acids, bases, and salts are so
intimately related to each other, it is very advantageous to give names
to the three classes in accordance with some fixed system. The system
universally adopted is as follows:

~Naming of bases.~ All bases are called _hydroxides_. They are
distinguis