640 Prof. EK. Rutherford on Slow 
The activity recovered by the 8 rays was, on the other hand, 
not appreciably changed by the high temperature. I urther 
heating, however, at a still higher temperature, caused a 
decrease of the activity measured by the 8 rays, showing that 
the 8 ray product was also volatile. These results show that 
the active matter consists of two kinds. The part which 
emits 8 rays is non-volatile at 1000° C., but the other part 
which emits a rays is almost completely volatilized at that 
temperature. 
Separation of the Constituents by means of a Bismuth Plate. 
The active matter of slow decay was obtained in solution 
by introducing dilute sulphuric acid into a glass tube in 
which the emanation from 30 milligrams of radium bromide 
had been stored for a month. The solution showed strong 
activity and gave out both « and @ rays, the latter, as in other 
cases, being present in an unusually large proportion. 
When a ’ polished bismuth disk was kept for some hours in 
the solution, it became strongly active. The active matter 
deposited on the bismuth gave out @ rays, but no trace of 
8 rays. After several bismuth disks had been successively 
left im the solution, the active matter, which emits @ 
rays, was almost completely removed. This was shown by 
evaporating down the solution after treatment. The 8 ray 
o 
activity remained unchanged, but the @ ray activity had 
been reduced to about 10 per ¢ cent. of its original value. The 
active matter deposited in the bismuth does not appreciably 
change in activity in the course of one month, and some 
observations point to the conclusion that there is not much 
change in five months. The observations in the latter case 
were, however, not precise enough to be sure that there was 
not a small percentage variation during that time. Hxperi- 
ments are now in progress to examine, with accuracy, the 
activity of the bismuth plate from time to time, and it is 
hoped that observations extending over the ensuing year will 
fix the rate of decay of this product, provided the rate of 
change is rapid enough to be measurable in a year’s interval. 
The results obtained in this way are in agreement with those 
co) 
deduced by heating the active deposit to a high temperature. 
‘The active deposit contains two kinds of matter, viz. :— 
(1) A product giving out only 6 rays, which is soluble in 
sulphuric acid, but non-volatile at 100U° C., and which 
is not deposited on bismuth. . 
(2) A product giving out only a rays, which is soluble in 
sulphuric acid, volatile at 1000° U., and is deposited 
from a solution on bismuth, 
