on the Absorption Coefficient of Iron for y Rays. 533 



In order to prevent a redistribution of the emanation in 

 the tube containing the radium owing to heating effects, it 

 was enclosed in a water-bath R and shielded from the furnace 

 by a sheet of asbestos. 



Fig. 1. 



R 



Experiments were made both while the iron was being 

 heated and while it was cooling, the temperature being 

 measured by means of a platinum-iridium thermo-couple. It 

 was found that the readings were not so consistent while 

 the block was being heated as while it was cooling. This 

 is due to the fact that the temperature of the room rose con- 

 siderably when heating was taking place, while when the 

 heating was stopped the hot air soon dispersed, and the 

 temperature did not vary while the iron was cooling. 



Results obtained in three experiments are given in 

 Table I. 



Table I. 



1 



Ionization. 



II. 



III. 



Temp. ° C. 



Tern,,. ° O. 



Ionization. 



Temp. ° C. 



Ionization. 



630 







3-55 



678 



357 



570 



3-38 



595 



3 60 



631 



3-48 



480 



3-36 



524 



3-52 



594 



347 



410 



335 



490 



350 



525 



3-48 



210 



336 



447 



350 



470 



3-48 



90 



3-36 



411 



3-50 



411 



3-49 



15 



333 



389 



350 



I 351 



3-48 







349 



3-50 



323 



3-40 







290 



3-50 



! 307 



178 



I 147 



3-47 

 347 

 3-47 



| 



' 







! 134 



3-45 



1 





