12 RADIO-ACTIVE SUBSTANCES [CH. 
same apparatus and under the same conditions led to the following 
results : 
a 
Uranium (containing a little carbon) 2°3 x 10-14 amperes 
Black oxide of uranium... bie 2°6 5 
Green “3 aie ae 1:8 x 
Acid uranic Redes BN aki 0-6 Bs 
Uranate of sodium... boo side 12 5 
Uranate of potassium vas dob 1:2 3 
Uranate of ammonia AP, ud 1133 ¥ 
Uranous sulphate... Sy ales 07 Leas 
Sulphate of uranium and potassium 0-7 5 
Acetate ae i isis 900 0-7 Bs 
Phosphate of copper and uranium 0:9 ty 
Oxysulphide of uranium ... ae 1:2 5 
The interesting point in connection with these results is that 
some specimens of pitchblende have four times the activity of the 
metal uranium; chalcolite, the crystallized phosphate of copper 
and uranium, is twice as active as uranium; and autunite, a 
phosphate of calcium and uranium, is as active as uranium. From 
the previous considerations, none of the substances should have 
shown as much activity as uranium or thorium. In order to be 
sure that the large activity was not due to the particular chemical 
combination, Mme Curie prepared chalcolite artificially, starting 
with pure products. This artificial chalcolite had the activity to 
be expected from its composition, viz. about 0°4 of the activity of 
the uranium. ‘The natural mineral chalcolite is thus five times as 
active as the artificial mineral. 
It thus seemed probable that the large activity of some of 
these minerals, compared with uranium and thorium, was due to 
the presence of small quantities of some very active substance, 
which was different from the known bodies thorium and uranium. 
This supposition was completely verified by the work of M. and 
Mme Curie, who were able to separate from pitchblende by purely 
chemical methods two active bodies, one of which in the pure state 
is over a million times more active than the metal uranium. 
This important discovery was due entirely to the property 
of radio-activity possessed by the new bodies. The only guide 
in their separation was the activity of the products obtained. In 
