Spcrion ILi., 1907. [9] Trans. R. S.C. 
II.—On the Radioactivity of Lead and Other Metals. 
By Proressor J. C. MCLENNAN AND V. E. Poux. 
(Read May 16, 1907.) 
In a paper in the Phil. Mag. of September, 1907, Eve stutes that 
while investigating the natural ionisation of air confined in vessels made 
of different metals, he found that 24 ions per cc. were generated per 
second when the receivers were made of copper, zinc, iron, and tinned 
iron, while 96 ions per cc. were regularly produced in air per second 
when the confining vessels were made of lead. 
The high conductivity of air contained in lead vessels has been 
frequently noted by other observers, but from Eve’s results it would 
appear either that lead contains some active impurity from which other 
metals are entirely free or else that lead possesses an intrinsic radiation 
very much stronger than that exhibited by other metals. 
The view that lead contains an active impurity is supported by a 
description in the Phys. Zeit. of November, 1906, of some experiments 
by Elster and Geitel in which they succeeded in extracting from lead 
oxide small quantities of an active substance which from its char- 
acteristics they were inclined to think was radium F. In this paper 
they state that they were unable to obtain any active emanation from 
the materials treated, and on this account they suggest that possibly 
the source of the radium F. can be traced to the presence of radium 
D in the lead. 
Since the decay period for radium D is forty years it would follow, 
if the high activity of lead is due to the presence of this radium product, 
that very old lead would exhibit an activity less intense than that which 
it emitted when freshly mined. 
Eve does not appear to have tested many different samples of lead, 
but if the explanation offered by Elster and Geitel of the high activity 
of lead be correct, one should expect to find that samples of lead selected 
at random from different localities would exhibit widely differing 
degrees of activity. 
This difference in the radioactivity of lead obtained from different 
sources was recently observed by the writers while making some measure- 
ments on the conductivity of air contained in metal vessels. 
In these experiments the metals examined were made up into 
cylinders 60 cm. long and 24 cm. in diameter, and from measurements 
with a sensitive quadrant electrometer on the saturation current through 
the air which they contained their activities were deduced. 
