26 Mr. J. Satterly on the Amount of Radium 



to west of our islands previous to this. The curves corre- 

 sponding to the maximum and mean wind values agree very 

 well, both going through the calm to the west of Ireland. 

 The minimum curve did not reach this calm, but was caught 

 in a feeble cyclone between Wales and Ireland, where it 

 performed a loop. The winds were gentle, spent a long time 

 over land, and reached Cambridge in fine warm weather, 

 thus accounting for a large emanation content. 



The average amount of Radium Emanation in the Air. 



In order to express the quantity of radium emanation in 

 the air in terms of the quantity of radium which would be 

 in radioactive equilibrium with it, it is necessary to carry 

 out comparison experiments, placing a radium solution of 

 known strength in series with one of the tubes. The arrange- 

 ment of fig. 2 is modified thus : — 



■*-Tube A— * Gauge A-*- /- — x 



Outside air — *■ (^ f Bottle J— Pump. 



^< Rad. Sol.— Tube B-~Gauge B— V_V 



The radium solution used was kindly given to me by 

 Prof. Rutherford, and its radium content was 3'14 x 10 -9 gm. 

 in the form of bromide. Before any " exposure " the solution 

 was cleared of all accumulation by bubbling air through it 

 lor an hour or two. The same volume of air is sent along- 

 each path at the same rate, therefore from the amounts of 

 emanation found from the two tubes we can get by subtraction 

 the value of the ratio 



emanation in a known volume of air 



emanation generated by the solution in a known time. 



The method is a comparative one, and the results are only 

 true if the same fraction of the total emanation is absorbed 

 by the charcoal, whatever be the emanation-content of the 

 air sent through the charcoal-tubes. Experiments made with 

 strong solutions indicated that with strong solutions satura- 

 tion occcurred, but with solutions giving about the same 

 amounts of emanation as those obtained in the experiments 

 fairly satisfactory results were obtained. 



The denominator in the fraction given above is the amount 

 of emanation yielded by a solution containing 3 , 14xl0~ 9 gm. 

 radium in the known time, t, of the experiment. To find 

 the mass of radium which would be in radioactive equilibrium 



