228 



- O. C. Lester — Emanation Electroscopes. 



Rutherford"^ and Owensf do not fit the conditions of the pres-- 

 ent work as they nsed radiations from layers of solid substances 

 in vessels of wholly different shape. The investigations of W. 

 Wilson;}: C. T. E. TTil son §, McLennan and Burton f and Patter- 

 son^i deal with the general question, but again under different 

 conditions. Furthermore they are not all in agreement. 



In order therefore to find how the activity at its maximum 

 varied with the pressure when emanation was mixed with air 

 in cylindrical vessels and incidentally also to see how nearly 

 the maxima were proportional to the amount of emanation 

 present, a series of tests were run in each chamber. The pro- 

 cedure followed was similar to that described by Madam Curie.*^ 

 However, what was here sought was a relation which would 

 give the " constant '' corresponding to any barometric pressure 

 and thus permit the reduction of the results of observation 

 immediately to curies, rather than a correction term to be 

 applied to the observed ionization current as in Madame Curie's 

 procedure. 



After the pressure in the chamber had been reduced to a 

 few centimeters a known amount of emanation was introduced. 

 During this operation the pressure increased to lO'^'" or 20'^'". 

 After the electroscope had stood charged for a little more than 

 three hours the activity was measured at various pressures 

 determined by a mercury monometer. The relations between 

 pressure and activity in vessel JS^o. 2 may serve as a typical 

 example. These relations for varying amounts of emanation 

 are shown in Table II and by curves in tig. 2. The figures in 

 the bod}^ of the table are maximum activities in divisions per 

 minute taken from the curves. In tig. 2 the actual experi- 

 mental data are represented by the continuous lines. 



Table II. 



Mgs. 

 Pitchblende 



5-Ot) 



10-55 ? 



15-85 



20-57 



25-20 



4(10 



500 



600 



00 



800 



3-14 



3 82 



4-40 



4-86 



.. 5-21 



6-42 



7-73 



8-78 



9-42 



; 9-71 



9-61 



11-49 



13-01 



14-02 



i 14-58 



13-10 



16-00 



17-90 



19-18 



i 19-95 



15-84 



19-31 ! 22-19 



Pressure 

 in mm. 



* Phil. Mag., vol. xlviii, p 109, 1899. 



f Ibid., p. 360. 



ilbid., (6), vol. xvii, p. 216, 1909. 



§Proc. Rov. Soc, vol. Ixix, p. 277, 1901. 



II Phvs. Rev., vol. xvi, p. 184, 1903. 



IT Phil. Mag.. (6), p. 231, 1903. 



** Traite de Radioactivite, vol. i, p. 286. 



