g2 The Philippine Journal of Science isu 



gested that the absorption is twofold: a quick effect, a surface 

 condensation, being followed by a slower effect, a diffusion into 

 the interior. If this is the true explanation, then it is to be 

 expected that for equal amounts of emanation passing over the 

 charcoal in different periods of time the amount absorbed will 

 be a direct rather than an inverse function of the time, since 

 the longer the time the greater the effect of the slow diffusion 

 into the interior. Taking Satterly's recorded results, we see 

 that this is not the case. For instance, no saturation was 

 found to be evident when the emanation from a solution 

 containing 6x10"^ gram of radium was passed over charcoal 

 for two hours and fifteen minutes, while an exposure of 

 twenty-one hours to the emanation from a solution containing 

 6.28x10-1° gram showed saturation to the extent mentioned 

 above, although in the first case a slightly greater amount of 

 emanation passed over the charcoal. It seems that the simple 

 explanation that we have advanced explains the whole phenom- 

 enon. For a long exposure, a part of the emanation absorbed 

 in the earlier hours of the experiment is caught up by the air 

 current and gradually carried onward and finally entirely out 

 of the tube. This will noticeably be the case when the charcoal 

 is packed in a short length of the tube, the best distribution 

 of a given weight of charcoal, as is also shown by our experi- 

 ments, being that obtained in a long tube of small bore- 



TESTS ON THE THIRD POINT 



Investigation of the third point was suggested by the state- 

 ment made by Satterly '- that "charcoal itself contains radium, 

 and if left to itself gradually accumulates radium emanation." 

 Several tests were made to determine whether the charcoal which 

 we were using gave any evidence of containing a trace of radium. 

 It seems to be contrary to one's expectation that an organic 

 substance like charcoal would contain radium unless it was 

 contaminated with radium salts during the process of making. 

 The results of our tests on this point are given in Table V. 



'""Phil. Mag. (1910), 20, 4. 



