VIIT] RADIO-ACTIVE EMANATIONS 227 
tion. The amount of emanation found was quite unchanged, 
whether carbon dioxide was sent over thoria in the manner de- 
scribed, or whether, keeping the other arrangements as_ before, 
an equally rapid current of air was substituted for it. The theory 
that the emanation is an effect of the excited activity on the 
surrounding medium is thus excluded. 
Experiments of a similar kind on the radium emanation were 
made later. A steady stream of gas was passed through a radium 
chloride solution and then through the reagent to be employed, 
into a testing-vessel of small volume, so that any change in the 
amount of emanation passing through could readily be detected. 
The radium emanation, like that of thorium, passed unchanged in 
amount through every reagent used. 
Later experiments. In later experiments by Sir William 
Ramsay and Mr Soddy!, the emanation from radium was exposed to 
still more drastic treatment. The emanation in a glass tube was 
sparked for several hours with oxygen over alkali. The oxygen 
was then removed by ignited phosphorus and no visible residue was 
left. When, however, another gas was introduced, mixed with 
the minute amount of emanation in the tube and withdrawn, 
the activity of emanation was found to be unaltered. In another 
experiment, the emanation was introduced into a magnesium lime 
tube, which was heated for three hours at a red heat. The 
emanation was then removed and tested, but no diminution in its 
discharging power was observed. 
The emanations of thorium and radium thus withstand chemical 
treatment in a manner hitherto unobserved except in gases of the 
argon family. 
150. Ramsay and Soddy (loc. cit.) record an interesting 
experiment to illustrate the gaseous nature of the emanation. 
A large amount of the radium emanation was collected in a 
small glass tube. This tube phosphoresced brightly under the 
influence of the rays from the emanation. The passage of the 
emanation from point to point was observed in a darkened 
room by the luminosity excited in the glass. On opening the 
stop-cock connecting with the Tépler pump, the slow flow through 
1 Proc. Roy. Soc. 72, p. 204, 1903. 
15—2 
