Ix] EXCITED RADIO-ACTIVITY 291 
the view, that polonium is in reality “induced” bismuth. At the 
same time, it has not yet been definitely settled whether Marck- 
wald’s radio-active tellurium contains the same active constituent 
as polonium or not. Taking the view that every case of induction 
is due to a removal with the inactive element of an active product 
of the radio-elements, some evidence will now be considered which 
points to the probability that polonium is a disintegration product 
of the element radium. 
It has been pointed out that Mme Curie was able to fractionate 
bismuth, made active in a radium solution, in the same way as 
polonium, z.e. that the active matter in the bismuth had chemical 
properties similar to polonium. Gjesel, in addition, showed that a 
platinum or bismuth plate placed in a radium solution acquired 
strong activity, and, like polonium, gave rise to a rays only. If 
the active bismuth or platmum decays at the same rate as 
polonium, it would be very strong evidence that polonium was a 
product of radium. Further experiments are, however, required 
on this point. 
It has been mentioned that bodies exposed for a long interval 
in the presence of the radium emanation, always retain about 
1/20,000 of their original activity. Giesel found that the residual 
activity of a platinum wire exposed in the presence of the radium 
emanation, gave out only a rays, and in that respect resembled 
polonium. 
The writer has recently found that active matter can be dis- 
solved by sulphuric acid from the inside of a glass tube, which 
has at one time contained the radium emanation. On evapora- 
ting the acid, an active deposit was left behind which gave out 
aand SB rays. The activity of this deposit, as far as observations 
have yet gone, has not decayed with the time. This active sub- 
stance gives out a far greater proportion of @ rays than either 
radium or thorium. The « rays showed about the same amount of 
absorption in aluminium foil as the @ rays from polonium, and 
possessed also the characteristic property exhibited by the 
polonium rays (section 90) of rapidly increasing absorption with 
thickness of matter traversed. It is thus possible that this 
active matter may contain polonium with another product giving 
rise to P rays. If it be assumed that the a rays, which are given 
19—2 
