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

LANTHANUM COMPOUNDS. 245

To separate the didymium from the lanthanum, sift magne-

sium oxide very slowly through wire gauze into the solution of

the nitrates, while this is kept boiling in a porcelain dish and is at

the same time stirred with a mechanical stirrer. The didymium

is precipitated together with a little lanthanum, but the greater

part of the lanthanum remains in solution free from didymium.

Control the separation by means of the spectroscope, and stop

adding magnesium oxide when a filtered portion of the solution,

in a layer 3 cm. thick, shows no trace of the didymium absorp-

tion bands.

Filter off and wash the precipitate and work it up for didy-

mium as directed below under (c). Precipitate the lanthanum

from the filtrate by means of ammonium carbonate solution,

after first adding 10 g. of ammonium chloride. In order to

remove all traces of magnesium, dissolve the precipitate in hydro-

chloric acid and reprecipitate it with ammonium carbonate.

Lanthanum Sulphate, La%{SOi) 3 -'dH 2 O. The ennea-hydrate

of lanthanum sulphate is readily obtained from lanthanum oxide,

which is itself prepared by igniting the carbonate. Following

the directions given for the preparation of thorium sulphate

(No. 170) treat the oxide with concentrated sulphuric acid, dis-

solve the anhydrous sulphate in ice-water, and then warm the

solution.

Determine the atomic weight of lanthanum by the sulphate

method (cf. p. 236).

Lanthanum Acetate, La(C 2 H 3 O 2 )s.Z H 2 O. Ignite 5 g. of lan-

thanum carbonate in a platinum crucible, pulverize the oxide thus

formed, and treat it in a flask with three times its weight of gla-

cial acetic acid; a reaction takes place with strong evolution of

heat, either of itself or upon gentle heating. Dissolve the result-

ing thick paste in as little water as possible, whereby only a very
small residue remains, and evaporate the nitrate until crystalliza-
tion takes place. Drain the crystals, wash them, first with 50%
alcohol, and then with pure alcohol, and dry them in the hot

closet.

Dependent preparation: Lanthanum Blue, No. 23.

Lanthanum Sulphide and Anhydrous Lanthanum Chloride can

be prepared according to the methods given for the correspond-

ing cerium compounds.