vu] RADIO-ACTIVE EMANATIONS 219 
of escape 1s continuous, the amount occluded will be much less than 
the amount for the non-emanating material. 
The phenomenon of occlusion of the radium emanation 1s prob- 
ably not connected in any way with its radio-activity, although this 
property has in this case served to measure it. The occlusion of 
hehum by minerals presents almost a complete analogy to the 
occlusion of the radium emanation. The helium is given off by 
fergusonite, for example, in part when it is heated and completely 
on dissolving the mineral. 
144. Similar results hold for thorium, but, on account of the 
‘rapid loss of activity of the emanation, the amount of emanation 
occluded in a non-emanating compound is very small compared 
with that observed for radium. If the prodtiction of the thorium 
emanation proceeds at the same rate under all conditions, the 
solution of a solid non-emanating compound should be accompanied 
by a rush of emanation greater than that subsequently produced. 
With the same notation as before we have for the thorium emana- 
tion, 
see ERE 
q@ 
This result was tested as follows: a quantity of finely powdered 
thorium nitrate, of emanating power 1/200 of ordinary thoria, 
was dropped into a Drechsel bottle contaiming hot water and the 
emanation rapidly swept out into the testing vessel by a current of 
air. The lonization current rose quickly to a maximum, but soon 
fell again to a steady value; showing that the amount of emanation 
released when the nitrate dissolves, is greater than the subsequent 
amount produced from the solution. 
The rapid loss of the activity of the thorium emanation makes 
a quantitative comparison like that made for radium very difficult. 
By shghtly altering the conditions of the experiment, however, a 
definite proof was obtained that the rate of production of emana- 
tion is the same in the solid compound as in the solution. After 
dropping in the nitrate, a rapid air stream was blown through the 
solution for 25 seconds into the testing vessel. The air stream was 
stopped and the ionization current immediately measured. The 
solution was then allowed to stand undisturbed for 10 minutes. 
