ric acid works and in the preparation of paint
pigments. Some alloys of lead, such as solder and pewter (lead and tin),
shot (lead and arsenic), and soft bearing metals, are widely used. Type
metal consists of lead, antimony, and sometimes tin. Compounds of lead
form several important pigments.

~Compounds of lead.~ In nearly all its compounds lead has a valence of 2,
but a few corresponding to stannic compounds have a valence of 4.

~Lead oxides.~ Lead forms a number of oxides, the most important of which
are litharge, red lead or minium, and lead peroxide.

1. _Litharge_ (PbO). This oxide forms when lead is oxidized at a rather
low temperature, and is obtained as a by-product in silver refining. It
is a pale yellow powder, and has a number of commercial uses. It is
easily soluble in nitric acid:

PbO + 2HNO_{3} = Pb(NO_{3})_{2} + H_{2}O.

2. _Red lead, or minium_ (Pb_{3}O_{4}). Minium is prepared by heating
lead (or litharge) to a high temperature in the air. It is a heavy
powder of a beautiful red color, and is much used as a pigment.

3. _Lead peroxide_ (PbO_{2}). This is left as a residue when minium is
heated with nitric acid:

Pb_{3}O_{4} + 4HNO_{3} = 2Pb(NO_{3})_{2} + PbO_{2} + 2H_{2}O.

It is a brown powder which easily gives up a part of its oxygen and,
like manganese dioxide and barium dioxide, is a good oxidizing agent.

~Soluble salts of lead.~ The soluble salts of lead can be made by dissolving
(Pb(C_{2}H_{3}O_{2})_{2}.3H_{2}O), litharge in acids. Lead acetate
called sugar of lead, and lead nitrate (Pb(NO_{3})_{2}) are the most
familiar examples. They are while crystalline solids and are poisonous
in character.

~Insoluble salts of lead; lead carbonate.~ While the normal carbonate of
lead (PbCO_{3}) is found to some extent, in nature and can be prepared
in the laboratory, basic carbonates of varying composition are much more
easy to obtain. One of the simplest of these has the composition
2PbCO_{3}.Pb(OH)_{2}. A mixture of such carbonates is called white lead.
This is prepared on a large scale as a paint pigment and as a body for
paints which are to be colored with other substances.

~White lead.~ White lead is an amorphous white substance which,
when mixed with oil, has great covering power, that is, it
spreads out in an even waxy film, free from streaks and lumps,
and covers the entire surface upon which it is spread. Its
disadvantage as a pigment lies in the fact