CERIC OXIDE FROM CEROUS OXALATE 283Procedure: It is rather difficult to adjust the temperature suc-
cessfully for the dry method. Place 33 grams litharge, 24 grams
of lead dioxide and 50 cc. of 6 N NaOH in a 600-cc. beaker. Stir
thoroughly and leave in a warm place (80°), striring when conven-
ient and adding water whenever the mass becomes dry, until the
contents have become bright red. Finally wash the red lead thor-
oughly by decantation, and rinse on to a gravity filter in a 5-inch
funnel. Let it drain over night. Lift the filter intact from the
funnel, open it out on paper towels, and leave it on the hot plate
until it is entirely dry. Detach the red lead from the paper by
bending the paper; transfer the dry material to a 150-cc. casserole
and heat it in a flame about 2 inches high, holding the casserole in
the hand and rotating it in the flame. At the correct temperature
(350-400°) the material becomes a dark reddish brown; after cool-
ing it is a much more brilliant red than before heating. Great
care must be taken to keep the material stirred during the heat-
ing so that the under layers do not become superheated and
changed to PbO. Preserve the preparation in a 2-ounce cork-
stoppered bottle.
QUESTIONS- If it is assumed that Pb2C>3 and PbgO* are lead metaplumbate
and lead orthoplumbate, respectively, write formulas to express
these facts. Write the formulas of the corresponding meta- and
orthoplumbic acids. - Warm a little of the red lead with nitric acid. What is the
residue, and what soluble salt is formed? Filter the mixture and
test the filtrate by diluting and adding a few drops of sulphuric
acid. - Heat a little of the red lead to a dull red heat on a thin piece
of iron.
PREPARATION 49
CERIC OXIDE FROM CEROUS OXALATE, CeO 2
Cerous oxalate, Ce2(C2O4) 3 -10H 2 O, is formed in the Welsbach
treatment of Monazite sands in the production of thorium nitrate,
and is the starting point in the preparation of nearly all cerium
salts. Since ceric oxide is more easily acted upon by common
reagents, it is often prepared as the first step in making other
salts from the oxalate.