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

TESTING FOR RADIOACTIVITY. 233

the solution with ammonia, and then treat it with a solution of
oxalic acid. This precipitates as oxalate any thorium that is
present. On treating the filtrate with ammonia, the hydroxides
of iron and aluminum are precipitated. The filtrate from the
first precipitation with ammonia may contain zinc and cobalt;
these metals should be precipitated with ammonium sulphide,
but they need not be separated from each other.
The filtrate from the ammonium sulphide group, on being
treated with ammonium oxalate, yields a precipitate of oxalates
of the alkaline earth metals.
That part of the ore which does not dissolve in nitric acid nor
during the subsequent treatment with aqua regia, should be fused
in a porcelain crucible with a mixture of sodium and potassium
carbohates. Extract the fusion with water, and wash the residue
until the filtrate no longer gives a test for sulphate. Dissolve
the carbonates in dilute nitric acid, and test the solution for lead
and the alkaline earth metals. The combined alkaline earths
should be separated from each other only when larger amounts of

pitchblende are worked up.

Testing for Radioactivity.

(a) Photographically. Fold a piece of black paper around a

photographic dry plate (in the dark room), so that the sensitive
side is covered with one thickness of the paper, and place the

whole in a box with the sensitive side up. Upon the plate

arrange samples of the original pitchblende and of the different

preparations obtained from it, each enveloped in a piece of paper.
Record the position of each specimen and then close the box.
Open it at the end of twenty-four hours and develop the plate in
the usual manner.
1

(b) Electroscopically. An approximate measure of aetivity

can be obtained with the aid of a sensitive gold-leaf electroscope.

A scale should be placed so that the distance between the gold

leaves can be read. The top of the electroscope should consist of

a metal plate, and above this at a definite distance a second metal

(^1) Uranyl nitrate, when prepared as above by the ether method, does not
show its full activity at once; its maximum intensity is "recovered" very
slowly, — one-half in twenty-two days.