Laboratory Methods of Inorganic Chemistry, 2nd English Ed. 1928

CERIUM COMPOUNDS. 243

1.1 parts of water. Evaporate the solution on the water bath

until it begins to crystallize, then, after 12 hours, drain the red

crystals of the double nitrate and wash them with a little nitric

acid. Evaporate the mother-liquor to obtain several further
fractions of crystals, and collect each fraction by itself. From

the last mother-liquor, precipitate the remaining cerium, together

with the impurities, by diluting with water and adding oxalic

acid.

Ignite a small portion from each of the crystal fractions on a

porcelain crucible cover over the blast lamp. The residue of

eerie oxide is pale yellow when the cerium preparation is pure;
if didymium is present it is of a reddish to chocolate-brown color.

Recrystallize the fractions that are shown to be impure by dissolv-

ing the double nitrate in 1.6 to 1.7 times its weight of 40% nitric

acid (3 parts HN0 3 , sp. gr. 1.4, and 2 parts H 2 O).
For the successful preparation of eerie ammonium nitrate it is
important to avoid reducing the tetravalent cerium. On this

account the nitric acid which is used as solvent must be boiled

for a short time in a flask in order to expel lower oxides of

nitrogen.

Cerium Sulphides.

Sulphides of cerium can be prepared by igniting cerous sulphate in a

stream of hydrogen sulphide. If the temperature remains below 720° the

dark-brown disulphide CeS 2 is formed; but if it is kept at a bright red heat,

dark cinnabar-red cerous sulphide, Ce 2 S 3 , is produced.

Add hydrogen peroxide to a boiling aqueous solution, con-

taining 20 g. of eerie ammonium nitrate, until the liquid is decolor-

ized; then add 7 g. of sulphuric acid and evaporate the solution

to dryness. Place the residue in a short combustion tube and

heat it in a stream of hydrogen sulphide which has been dried

with calcium chloride. Heat the tube in a combustion furnace

first to a dull red and later to a bright red, and occasionally

revolve the tube on its long axis.

If cerous sulphide has been formed, the product dissolves in

hydrochloric acid without residue; if the product contains cerium

disulphide, free sulphur separates on this treatment. Test the

hydrochloric acid solution with barium chloride to show whether

the sulphate has been completely decomposed.