Ionization produced by Heated Salts. 373 



of salt vapour between the outer glass walls and the gauze. 

 The inner electrodes, centralized with respect to the outer 

 ones, were of platinum wire 0*2 mm. in diameter. Each 

 wire was sealed in glass; the lower 6 cm. only were left 

 exposed. 



Fiff. 1. 



TO PUMP 



The double-tube apparatus was heated in an electric oven, 

 and was inserted into it some 10 centimetres above the 

 electrodes. The furnace was first heated some 50° G. higher 

 than the temperature desired, the tube was then introduced 

 and the required temperature obtained in 3-5 minutes. 

 This is important, particularly in determining the initial 

 stages of the rise or decay of the ionization with time. By 

 means of control resistances it was possible to keep the 

 temperature constant within 5 degrees over several hours of 

 experimentation. 



Before each test the main tubes and the electrodes 

 were thoroughly cleansed with nitric acid, sulphuric acid, 

 alcohol and ether mixture and distilled water, and then 

 slowly dried. At temperatures between 350° C. and 500° C. 

 and with potential of ± 200 volts applied at the outer 

 electrodes, leakage currents were obtained which ranged in 

 value from 1 x 10" 13 to lxlO -11 ampere. These currents 



