O48. Prof. E. Rutherford on Slow 
the activity on separation, measured by the number of electrons 
expelled per second, should be 25 times as great as from an 
equal weight of radium. The a ray activity produced in it 
should at any time be capable of separation by adding a 
bismuth plate to a solution of the substance. 
Radium /.—The substance should emit only «& rays, and 
its activity should fall to half value in about one year. 
Since its rate of change is about 1000 times as great as 
radium, the substance, weight for weight, should emit about 
1000 times as many @ particles as freshly prepared radium, 
and about 250 times as many as from radium about one 
month old. The activity measured by the electric method 
will probably be about 100 times as great as that of pure 
radium. 
It is now necessary to consider the question whether the 
substances radium D and E have been previously separated 
from pitchblende, and are known by other names. In regard 
to radium D, there is some doubt whether it has been 
previously separated. It is possible that it is the radioactive 
constituent present in the radio-lead of Hoffmann, for he 
states that this substance emits a large amount of @ rays. 
On the other hand, the radio-lead prepared by other observers 
lost its activity rapidly with the time. 
Jn regard to radium E, I think there is little doubt that it 
is the radioactive constituent present in the so-called radio- 
tellurium of Mareckwald*. It will be recalled that Marckwald 
obtained a deposit of radioactive matter on a bismuth plate 
introduced into a solution of pitchblende. ‘This active 
bismuth gave out only a rays. The active matter was 
associated with tellurium and was, in consequence, called 
radio-tellurium. In later observations Marckwald has shown 
that tellurium is merely an impurity, and has devised a 
method of concentrating the radioactive matter. 
The radioactive constituent in radio-tellurium and that in 
radium E are very analogous in chemical and radioactive 
properties, for both emit «rays, and both are deposited on a 
bismuth plate introduced into the active solution. In addition, 
T have found that the « rays from the two substances are 
identical in their power of penetration through aluminium. 
The radio-tellurium was obtained from Dr. Sthamer of 
Hamburg, in the form of a thin film of the active matter 
deposited on the surface of a polished bismuth plate. I was 
unable to detect any difference in the penetrating power of 
the rays frem radium E and radio-tellurium, although the 
intensity of the radiation was reduced to a few per cent. by 
* Berichte d, D. Chem, Ges, p. 2285 (1902). 
