by ol Particles from Radium Emanation. 907 



reduce the natural activity owing to the presence of 

 radium I), the walls being 8 mm. thick. The windows 

 were protected from stray radiation by cylindrical tubes of 

 lead of the same thickness, which projected about 6 cm. 



Fi£. 1. 



50 £ To £arth 





from the electroscope. The lead base, through which the 

 radiations to be examined had to pass to enter the electro- 

 scope, could be varied in thickness, the range being 1*7 mm. 

 to 18*5 mm. 



Since the products radium B and radium C emit hard 

 primary 7-rays, it is imperative that the radium emanation, 

 which is examined in the tube A, should be pure and free 

 from active deposit. The precautions adopted to ensure this 

 were as follows. Purified emanation was forced into the 

 tube B, into which are sealed two electrodes, the negative 

 being made of platinum foil about 4 sq. cm. area. This tube 

 contains a large number of pieces of broken glass to increase 

 the surface area, as the deposition is largely a surface effect. 

 To the tube A was attached a side tube P for evacuation 

 purposes and a delicate constriction, which could be sealed 

 off rapidly, was* placed at 0. Glass-wool plugs were placed 

 at W, W to arrest any solid particles of active deposit which 

 might be carried over with the emanation into A. The 

 tube A and its connexions were then sealed on to tube B at 

 the section XX, and with the tap T closed, the whole as Ear 

 as T was evacuated through P, and sealed off at 0. The 

 tube A, which was of ten times the capacity of tube B, was 

 closed with a ground-glass stopper greased with phosphoric 



302 



