Radium Emanation by Coconut Charcoal. 781 



conditions, the amount of emanation absorbed by the charcoal 

 is practically proportional to the emanition content of the 

 air sent through the charcoal. For stronger solutions as 

 used in (1),(2), (3), the amount absorbed does not increase 

 in the same proportion as the emanation content o£ the air ; 

 it certainly looks as if the charcoal were approaching 

 saturation. 



The strength of the solution ^E x is very nearly the same as 

 that of a solution containing 3'1I x 10 ~ 9 gm. radium which 

 was given to the author by Professor Rutherford; for that 

 solution gave me a reading 2*5 for a 2-hours run *. The 

 solution JE X therefore contains about 3 x 10~ 9 gm. radium, 

 and the emanation it would yield in 2\ hours would have a 

 volume of 3 x 10 ~ 14 c.c. It is hard to imagine that charcoal 

 would be saturated even with a volume many hundred times 

 this t ; but it must be remembered that an air-stream is 

 passing through the charcoal all the time and that this air 

 has two effects : (1) it is absorbed by the charcoal, thus 

 leaving less room for any other gas, and (2) it tends to blow 

 out any otiier gas that has been absorbed. 



It follows that if for solutions of strengths 3xl0~ 9 and 

 6x 10~ 9 gm. radium the amount absorbed is proportional to 

 the strength of the solution, this proportionality would also 

 hold for weaker solutions and also for the radium content in 

 the air, thus justifying the method of calculation employed 

 in my paper in the Phil. Mag. of October 1908. 



II. 



Experiments made to find out whether the fraction of the 

 emanation absorbed* when the emanation is supplied 

 from a constant source by a steady stream of air } is 

 independent of the time of exposure. 



In this series of experiments two silica tubes, A and B, 

 (each (30 cms. long, 8*0 sq. cm. in cross-section, and con- 

 taining about 130 gm. of coconut charcoal in the central 

 foot) were coupled up as shown in the accompanying diagram 



-Tube A or 13 — Gauge A or B N 



Outside / \ -° 



air. "*■ \ / > ~ 



^Radium Solution Tube B or A Gauge B or A 



* Phil. Mag. Oct. 1908, p. 599. 



t At 10° 0. one gram of coconut-charcoal absorbs 3xl0~ 5 c. c. of 

 radium emanation (Rutherford, Manch. Lit. Phil. Soc. Dec. 1908). This 

 is, of course, a statical result. 



