232 Barss — Ionization by Collision in Gases and Yapors. 



Fig. 1. 



^*Hl-- []«■■■* earth 

 V 



of the pinion. JJ is an earthed brass gauze to counteract any 

 electrical effects from the surface of the glass jar. The open- 

 ing D in the top BB was connected to a Topler pump, an open 

 manometer and a MacLeod gauge, so that all pressures up to 

 an atmosphere could be measured. The opening C was con- 

 nected to the vapor or gas supply. Connections from the 

 chamber to the pump and to the gas supply were made of glass 

 tubing. The joints between brass and glass were made air- 

 tight by sealing with rubber stopcock grease and soft wax. 

 Connections from the chamber to the electrometer were pro- 

 vided with earthed guard tubes. A thin coating of powdered 

 uranium oxide attached to the upper surface of the lower plate 

 provided a suitable source of alpha radiation. 



The experiments were conducted in the following manner: 

 The rod connecting the plate Gr to the electrometer was earthed 



