marily due to the
slight extent to which either the acid or the base formed is
dissociated, several other factors have an influence upon the extent to
which it will take place.

1. _Influence of mass._ Since hydrolysis is a reversible reaction, the
relative masses of the reacting substances influence the point at which
equilibrium will be reached. In the equilibrium

BiCl_{3} + 3H_{2}O <--> Bi(OH)_{3} + 3HCl

the addition of more water will result in the formation of more bismuth
hydroxide and hydrochloric acid. The addition of more hydrochloric acid
will convert some of the bismuth hydroxide into bismuth chloride.

2. _Formation of insoluble substances._ When one of the products of
hydrolysis is nearly insoluble in water the solution will become
saturated with it as soon as a very little has been formed. All in
excess of this will precipitate, and the reaction will go on until the
acid set free increases sufficiently to bring about an equilibrium. Thus
a considerable amount of bismuth and antimony hydroxides are
precipitated when water is added to the chlorides of these elements. The
greater the dilution the more hydroxide precipitates. The addition of
hydrochloric acid in considerable quantity will, however, redissolve the
precipitate.

~Partial hydrolysis.~ In many cases the hydrolysis of a salt is only
partial, resulting in the formation of basic salts instead of the free
base. Most of these basic salts are insoluble in water, which accounts
for their ready formation. Thus bismuth chloride may hydrolyze by
successive steps, as shown in the equations

BiCl_{3} + H_{2}O = Bi(OH)Cl_{2} + HCl,

BiCl_{3} + 2H_{2}O = Bi(OH)_{2}Cl + 2HCl,

BiCl_{3} + 3H_{2}O = Bi(OH)_{3} + 3HCl.

The basic salt so formed may also lose water, as shown in the equation

Bi(OH)_{2}Cl = BiOCl + H_{2}O.

The salt represented in the last equation is sometimes called bismuth
oxychloride, or bismuthyl chloride. The corresponding nitrate,
BiONO_{3}, is largely used in medicine under the name of subnitrate of
bismuth. In these two compounds the group of atoms, BiO, acts as a
univalent metallic radical and is called _bismuthyl_. Similar basic
salts are formed by the hydrolysis of antimony salts.

EXERCISES

1. Name all the elements so far studied which possess allotropic forms.

2. What compounds would you expect phosphorus to form with bromine and
iodine? Write the equations showing the action of water on these