XI] AND OF ORDINARY MATERIALS 361 
air mixed with the radio-active emanation was condensed. The 
liquefied gas was allowed to evaporate, and the earlier and last 
portions of the gas were collected in separate vessels. The final 
portion was found to be about 30 times as active as the first portion. 
An examination of the radio-active properties of the active 
gases so obtained has been made by Adams!. He found that the 
activity of the emanation decayed in an exponential law with the 
time, falling to half value in about 3-4 days. This is not very 
different from the rate of decay of the activity of the radium 
emanation, which falls to half value in a little less than four days. 
The excited activity produced by the emanation decayed to half 
value in about 35 minutes. The decay of the excited activity 
from radium is at first irregular, but after some time falls off in an 
exponential law, diminishing to half value in 28 minutes. Taking 
into account the uncertainty attaching to measurements of the 
very small ionization observed in these experiments, the results 
indicate that the emanation obtaimed from well water in England 
is similar to, 1f not identical with, the radium emanation. Adams 
observed that the emanation was slightly soluble in water. After 
well water had been boiled for some time and then put aside, it 
was found to recover its power of giving off an emanation with 
time. The amount obtained after standing for some time was 
never more than 10 per cent. of the amount first obtained. Thus 
it is probable that the well water, in addition to the emanations 
mixed with it, has also a slight amount of a permanent radio-active 
substance dissolved in it. Ordinary rain water or distilled water 
does not give off an emanation. 
Bumstead and Wheeler* have recently made a very careful 
examination of the radio-activity of the emanation obtained from 
the surface water and soil at New Haven, Connecticut. The 
emanation, obtained from the water by boiling, was passed into 
a large testing cylinder, and measurements of the current were 
made by means of a sensitive electrometer. The current gradually 
rose to a maximum after the introduction of the emanation, in 
exactly the same way as the current increases in a vessel after the 
introduction of the radium emanation. The decay of activity of 
1 Phil. Mag. Nov. 19038. 
2 Amer. Journ. Science, 17, p. 97, Feb. 1904. 
