730 Mr. A. S. Eve on the Amount of Radium Emanation 



that the first tube A retained more than B and C, although 

 the current through A was twice as fast as through B or C. 

 All the emanation was not driven off by the first heating ; at 

 the second heating, tw-o days later, the amounts obtained 

 were 



A. B. C. Total. 



7-3 3-7 4*4 15-4 



The amount of emanation used in this case was large, and 

 would at a maximum have caused the gold-leaf to move at a 

 rate measurable by about 1000 divisions a minute. But in 

 the 3* 7 days only half this amount would be generated. It 

 took six heatings and several days' rest to free the charcoal 

 from this heavy dose of emanation. 



Medium Solution. 1*57 X 10~ 9 . 

 The amounts obtained were 



A. B. C. Total. 



•53 -40 -41 1-34 



from which must be deducted* 36 due to the emanation in the 

 air pulled through. Therefore 1*57 x 10 ~ 9 gram caused 

 0*98 D/m under the conditions of the experiment. This is, 

 again, about 20 per cent, of the possible maximum. 



The amounts caught by the three tubes were nearly equal, 

 and in a number of experiments with solutions of this strength 

 I found that the leading tube A usually stopped but little 

 more than B or C, about 25 to 30 per cent. 



Weak Solution. lO" 10 . 



The effect was in this case small and difficult to measure, 

 about '06 division a minute. 



These three calibrations are in fair agreement and give, 

 per 10~ 10 gram, 



•066 J) I in for the strong solution, 

 '062 „ „ medium „ 

 •06 „ „ weak „ 



The mean value is '063 D/m per 10~~ 10 gram of radium. 



But it will be remembered that 1*56 cb.m. of air gave 



•125 D/m. 



Hence 1 cb.m. of air contains the emanation from 



*125 10~ 10 



— rrrX- ' _ gram, or from 127 x 10 -12 gram of radium. 



1-56 -063 s ' & 



Summary. — The amount of emanation per 1 cb.m. of air 



