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

238 COMPOUNDS OF THE RARE ELEMENTS.

ness on the water bath, dissolve the residue in hot water, and

precipitate thorium hydroxide from the boiling solution by add-

ing sodium thiosulphate.

1

To precipitate the rare earths, add sodium carbonate to the

filtrate from the thorium hydroxide, drain and wash the pre-

cipitate, and dry it in the hot closet. This product may be

worked up according to No. 171.

Purification of the Thorium. Dissolve the thorium precipi-

tates in hydrochloric acid, adding, if necessary, a little nitric

acid; evaporate the solution to dryness, take up the residue in

water, filter if necessary, and treat the solution at 60° with a

solution of sodium thiosulphate. Collect the precipitate on a

filter, wash it with water containing some ammonium nitrate (as

it has a tendency to pass into colloidal solution), and ignite it to

thorium dioxide.

Thorium Sulphate. Heat the thorium oxide with concen-

trated sulphuric acid in a porcelain crucible until the excess of

acid has been expelled, moisten the residue with a few drops

more of sulphuric acid and heat it as before, but avoid bringing

it to a red heat. Pulverize the thorium sulphate, which should

be free from acid salt, and add it gradually, with vigorous

stirring, to five times its weight of ice-water. If, after a little

while, a considerable residue remains undissolved, remove it and

subject it again to the treatment with concentrated sulphuric

acid.

By warming the filtered solution to 30 — 35°, thorium sulphate

octohydrate, Th(SO 4 ) 2 • 8 H 2 O, together with a little enneahydrate,

Th(SO 4 ) 2 • 9 H 2 O, is caused to separate. Maintain the solution

at this temperature, and allow it to evaporate until all of the

salt has separated. Drain the crystals, wash them with a

(^1) The salts of quadrivalent thorium are more easily hydrolyzed than those
of the tervalent rare-earth metals. Thus thorium hydroxide is precipitated
while the salts of the trivalent metals remain unchanged. The principle of
this separation is similar to that of the basic acetate method used in analyti-
cal chemistry.
According to another method, the solution is warmed to 60 to 70° together
with an excess of a 10% hydrogen peroxide solution; the thorium and some
cerium are thrown down in the form of a flocculent precipitate which can be
easily filtered.