282 ELEMENTS OF GROUP IVview is strengthened by the behavior of the substance when treated
with nitric acid — part of the lead dissolves to give lead nitrate,
while the other part is left as lead dioxide,
Pb 2 (Pb0 4 ) + 4HNO 3 ^2Pb(NO 3 ) 2 + H 4 (Pb0 4 )
»PbO 2 + 2H 2 O
The following procedures should yield a product of nearly the
composition Pb 3 C>4. This substance, under the commercial name
of minium, finds use as a red pigment.DRY METHOD
Material: lead monoxide (massicot), PbO, 25 grams.
Apparatus: iron or aluminum plate 2-4 mm. thick,
ring burner,
iron spatula.
Procedure: Spread 25 grams of lead monoxide in a thin layer
on an iron or aluminum plate 2-4 mm. thick. Either use the
variety of lead oxide which has not been fused and is known under
the name of massicot, or use lead carbonate, which on being heated
yields a very pure and finely divided lead monoxide. Heat the
lead oxide over a ring burner so adjusted that the flames do not
quite touch the metal plate. The plate must be kept just below
a perceptible red heat. Continue the heating for 6 hours or more
and turn over the powder frequently with an iron spatula. When
the change is complete, the product is dark brown when hot, a
bright scarlet-red when partly cooled, and a somewhat less brilliant
red when entirely cold.
WET METHOD
Materials: lead monoxide (litharge) PbO, 33 grams = 0.15
F.W.
lead dioxide PbO 2 ,24 grams = 0.1 F.W.
6iVNaOH.
Apparatus: 600-cc. beaker.
5-inch funnel.
150-cc. casserole,
iron ring and ring stand.
Bunsen burner,