i ¢ 
[eve] RADIUM EMANATION IN ATMOSPHERE 21 
were obtained, and the charcoal was prepared with great precaution, and 
finally some tubes of charcoal were obtained free from radium. 
The first series of experiments made with a single tube of charcoal 
gave minute and uncertain results. The current of air was, therefore, 
divided, so that it passed through three tubes placed in parallel, each 
containing 7 grams of charcoal. A comparison was made between the 
emanation obtained from the tubes, (1) after the current had run for 
the number of days specified, (2) after the tubes had rested. The 
results are given in scale divisions per minute of the electroscope, the 
natural leak of which was .065. 
No. of Days. Run. Rest. 
3 Horse .095 
3 118 aba 
3 aly, .085 
4 1 AT 
3 .083 
A solution containing 10—1° grams of radium was then placed in 
a flask, and the emanation from it carried for 3 days at the same speed 
as before through the carbon tubes. These when heated gave emanation 
measuring .22 divisions a minute. And since seven-tenths of a cubic 
metre had been drawn through the tubes in three days, it may be readily 
deduced that 1 cb. km. of the atmosphere contains .03 grams Ra Br,. 
My result by active deposit method was 44 times larger than this. 
It will be seen in the above table that the results obtained for a 
run” were always greater than for a “rest,” but the difference be- 
tween them, on which the result depends, averaged .03, a small quan- 
tity, about half the magnitude of the natural leak. It was, therefore, 
desirable to work on a larger scale. 
Three iron pipes were prepared 37 em. long and 4 cm. in diameter. 
Each contained 220 grams of finely divided charcoal. Air from out- 
side the building was drawn bv a water pump through H.SO, and 
CaCl, and was passed through the three iron tubes arranged in 
parallel. By this means the speed could be increased threefold, and 
yet the volume and cross-section of the absorbing charcoal was 
sufficiently large for good results. A convenient speed was found to he 
