her metals. It melts at a low temperature (270 deg.)
and has a density of 9.8. It is not acted upon by the air at ordinary
temperatures.

~Chemical properties.~ When heated with the blowpipe on charcoal, bismuth
gives a coating of the oxide Bi_{2}O_{3}. This has a yellowish-brown
color which easily distinguishes it from the oxides formed by other
metals. It combines very readily with the halogen elements, powdered
bismuth burning readily in chlorine. It is not very easily acted upon by
hydrochloric acid, but nitric and sulphuric acids act upon it in the
same way that they do upon copper.

~Uses.~ Bismuth finds its chief use as a constituent of alloys,
particularly in those of low melting point. Some of these melt in hot
water. For example, Wood's metal, consisting of bismuth, lead, tin, and
cadmium, melts at 60.5 deg..

~Compounds of bismuth.~ Unlike the other elements of this group, bismuth
has almost no acid properties. Its chief oxide, Bi_{2}O_{3}, is basic in
its properties. It dissolves in strong acids and forms salts of bismuth:

Bi_{2}O_{3} + 6HCl = 2BiCl_{3} + 3H_{2}O,

Bi_{2}O_{3} + 6HNO_{3} = 2Bi(NO_{3})_{3} + 3H_{2}O.

The nitrate and chloride of bismuth can be obtained as well-formed
colorless crystals. When treated with water the salts are decomposed in
the manner explained in the following paragraph.

HYDROLYSIS

Many salts such as those of antimony and bismuth form solutions which
are somewhat acid in reaction, and must therefore contain hydrogen ions.
This is accounted for by the same principle suggested to explain the
fact that solutions of potassium cyanide are alkaline in reaction (p.
210). Water forms an appreciable number of hydrogen and hydroxyl ions,
and very weak bases such as bismuth hydroxide are dissociated to but a
very slight extent. When Bi^{+++} ions from bismuth chloride, which
dissociates very readily, are brought in contact with the OH^{-} ions
from water, the two come to the equilibrium expressed in the equation

Bi^{+++} + 3OH^{-} <--> Bi(OH)_{3}.

For every hydroxyl ion removed from the solution in this way a hydrogen
ion is left free, and the solution becomes acid in reaction.

Reactions of this kind and that described under potassium cyanide are
called _hydrolysis_.

DEFINITION: _Hydrolysis is the action of water upon a salt to form an
acid and a base, one of which is very slightly dissociated._

~Conditions favoring hydrolysis.~ While hydrolysis is pri