1] RADIO-ACTIVE SUBSTANCES 23 
is precipitated with the iron group, and appears to be very closely 
allied in chemical properties to thorium, though it 1s many thousand 
times more active. It is very difficult to separate from thorium 
and the rare earths. Debierne has made use of the following 
methods for partial separation : 
(1) Precipitation in hot solutions, slightly acidulated with 
hydrochloric acid, by excess of hyposulphite of soda. The active 
matter is present almost entirely in the precipitate. 
(2) Action of hydrofluoric acid upon the hydrates freshly 
precipitated, and held in suspension in water. The portion 
dissolved is only slightly active. By this method titanium may 
be separated. 
(3) Precipitation of neutral nitrate solutions by oxygenated 
water. The precipitate carries down the active body. 
(4) Precipitation of insoluble sulphates. If barium sulphate, 
for example, is precipitated in the solution containing the active 
body, the barium carries down the active matter. The thorium 
and actinium are freed from the barium by conversion of the 
sulphate into the chloride and precipitation by ammonia. 
In this way Debierne has obtained a substance comparable 
in activity with radium. The separation, which is difficult and 
laborious, has so far not been carried far enough to bring out 
any new lines in the spectrum. Actinium gives out easily ab- 
sorbed and penetrating deviable rays lke those of radium, 
and also a radio-active emanation!, which is more allied to the 
emanation of thorium than to that of radium. The emanation 
has a distinctive rate of decay; it loses its activity in the course 
of a few seconds, while the thorium emanation loses half its activity 
in one minute. The distinctive character of the radiations and 
emanations, together with the permanence of the activity, make 
it very probable that actinium will prove to be a new element 
of very great activity. 
21. Griesel? also has obtained from pitchblende a radio-active 
substance which in many respects is similar to the actinium of 
Debierne. The active substance belongs to the group of cerium 
1 ¢, R. 136, p. 446, 1903. 
2 Ber. deutsch. chem. Ges. p. 3608, 1902; p. 342, 1903. 
