642 Miss M. S. Leslie : Comparison of the Coefficients of 



repeated, but with the difference that a small quantity o£ a 

 strong radiothorium product was used instead o£ thorium 

 hydroxide. Since the activities were not determined for at 

 least five hours after the removal of the plates from the dif- 

 fusion vessel, no difficulties would arise owing to the presence 

 of radium emanation, because any radium active deposit 

 would then have disappeared. 



In the first experiments made the activities were eighty or 

 ninety times those obtained in the former experiments, and 

 the resulting value for P x D was found to be very high. 



P. 



PXD (corrected). 



77*1 cm. 



8-63 "j exposures of 



77-1 „ 



10-48 U or 6 hours 



76-6 „ 



9-34 J only. 



76-6 „ 



8-70 



76-1 „ 



9-19 



76-0 „ 



8-29 



75-8 „ 



8-88 



Mean of last four 



. . 8-77 



The value of D in air at 76 cm. pressure and 15° C=i'll&. 



The supply of emanation was cut down by covering the 

 radiothorium with perforated tinfoil and layers of blotting- 

 paper. The activities were now diminished to about twenty 

 times those obtained from the hydroxide, and it was found 

 that the value of P x D had also decreased. 



P. PxD (corrected). 



76-7 cm. 8-76 



76-0 „ 8-15 



76-0 „ 8-48 



75-9 „ 8-21 



75-9 „ 8-17 



75-8 „ 9-38 



Mean . . 8*51 

 The value of D in air at 76*0 cm. pressure and 15° C. = -112. 



A further diminution of emanation until it was only about 

 five or six times that obtained from thorium hydroxide was 

 again followed by a decrease in the value of the product 

 PxDj but only to a slight extent. 



