[BOYLE] TEMPERATURE AND VELOCITY OF GAS CURRENT 111 
sufficiently free by the air at low speeds. The theory assumes that the 
emanation atoms are removed as fast as they are produced whatever the 
speed of the air current; it may be that it is necessary for the air to 
move at a certain rate before this is altogether correct. 
Conclusion. 
__ In the discussion in this paper concerning the absorption of thorium 
emanation by cocoanut charcoal, an attempt is made to explain the 
facts observed by experiment. As before stated, the experiments are 
preliminary, and consequently, the deductions had better be considered 
as tentative until the experimental tield is widened. 
We can summarize the paper as follows :— 
(1) With an experimental arrangement such as described, the per 
cent absorption of thorium emanation by cocoanut charcoal 
in a granulated form, and at a constant temperature, is 
ss 
given by a formula, 100 (1 - e 4 ), where 
q is the flow in C.C. per second of the air carrying the 
emanation. 
V, is the actual volume of the charcoal, 
and s is a coefficient depending on the absorptive power, 
and on the temperature of the charcoal. (It is not 
yet determined if s depends in any way on the size of 
the charcoal grain). 
An exception must be made to the above result in the case of low 
speeds of the air current; for speeds less than 6 ec. per second the 
absorption is greater than that given by the formula. 
(2) The absorption is greatly affected by the temperature of the 
charcoal; the lower the temperature of the charcoal the 
better absorbent it becomes. If ds is the change in the 
coefficient s corresponding to a small increase of temperature 
dsp 
dt, then — = is a constant between —782 and 100° C, 
(3) There is an indication that at temperature higher than 310° C., 
s will be zero, that is, the charcoal will be completely non- 
absorbing. 
I desire to express my thanks to Professor Rutherford for suggest- 
ing this piece of work, and for his interest and kindness while it was 
in progress. 
