The Radioactivity of Potassium, etc. 
557 
The Radioactivity of Potassium, with special reference to 
solutions of its salts. By Norman Campbell, M.A., Trinity 
College. 
[Read 18 May 1908.] 
I. Attempt to separate the activity. 
| 1. In former communications to the Society* the remarkable 
activity displajmd by the salts of potassium has been described. 
It appears to be due to the emission of /3 rays, some of which 
approach in penetrating power the /3 rays of uranium, and to be 
closely connected with the presence of the element potassium. 
All the salts examined showed the activity in an amount approxi- 
mately proportional to the potassium content, but no other bodies 
examined seemed to emit similar rays. 
There remains for decision the important question whether the 
association with potassium of the element (for all analogy leads 
to the belief that it must be an element), which is responsible for 
the activity, is fortuitous or essential. The association may be 
due merely to a close similarity in chemical properties between 
the potassium and the active element, or it may be due to the fact 
that the active element is potassium itself or that it is descended 
from that element as radium is descended from uranium. 
Whichever of these alternatives is true it becomes important 
to try to separate from a potassium salt some part of its activity. 
The experiments about to be described were undertaken with that 
object : complete failure to effect any separation has been their 
result, but incidentally phenomena have been observed which are 
of some interest. 
§ 2. The measurement of the activity of the preparations 
was made in all cases in the vessel described on p. 212 of the 
first paper quoted above. The preparations were placed in trays 
of an area of 500 cm. 2 and a depth of 0*5 cm., which they filled 
completely. The current through the vessel, when the trays were 
placed beneath the large window (about 1450 cm. 2 ) of thin 
aluminium leaf, was compared by means of the compensation 
method previously used with the current when the trays were 
replaced by similar empty trays. The probable error of a single 
observation was about one of the arbitrary units used in the 
Proc. Camb. Phil. Soc. xiv. 1. 15 — 21 and xiv. 2. 211 — 210. 
