should
be less than that of uranium. On the contrary, it is several times
greater. Natural and artificial chalcolite also show a marked
difference in favor of the former. The supposition was a natural one,
therefore, that these minerals contained small quantities of an
element, or elements, undetected by ordinary analysis and having a
much greater activity than uranium. Similar results were obtained in
the examination of thorium minerals and thorium salts.

Discovery of Polonium

Following up this supposition, M. and Mme. Curie set themselves the
task of separating this unknown substance. Starting with pitchblende,
a systematic chemical examination was made. This is an exceedingly
complex mineral, containing many elements. The processes were
laborious and demanded much time and minute care. They need not be
described here. It is sufficient to say that along with bismuth a very
active substance was separated, to which Mme. Curie gave the name of
polonium for Poland, her native land. Its complete isolation is very
difficult and sufficient quantities of the pure substance have not
been obtained to determine its atomic weight and other properties, but
some of the lines of its spectrum have been determined. Chemically it
is very closely analogous to bismuth.

Discovery of Radium

In a similar manner a barium precipitate was obtained from pitchblende
which contained a highly active substance. The pure chloride of this
body and barium can be prepared together and then separated by
fractional crystallization. To the new body thus found the name of
radium was given. It is similar in chemical properties to barium. Its
atomic weight has been determined by several careful investigators and
is accepted as 226. Its spectrum has been mapped and its general
properties are known. It is a silvery white, oxidizable metal. In one
ton of pitchblende about 0.2 gram of radium is present; this is about
5000 times greater than the amount of polonium present. The activity
of the products was depended upon as the guide in these separations.
The radium found is relatively enormously more active than the
pitchblende or uranium.

Other Radio-active Bodies Found

In the above separations use was made of relationships to bismuth and
barium. Similarly, by taking advantage of chemical relationship to the
iron group of elements, another body was partially separated by
Debierne, to which he gave the name actinium. Boltwood discovered in
ur