Ionization produced by. Heated Salts, 



383 



chemical reaction * between the vapours and the heated 

 electrodes may vitiate the true ionization effects. 



In order, then, to obtain decisive tests as to the presence of 

 a true negative ionization and to eliminate effects due to 

 chemical action, the containing vessel was provided with an 

 inner air-cooled metallic electrode and an outer hot non- 

 metallic electrode. The apparatus used is shown in fig. 5. 



Fig. 5. 



TO ELECTROMETER 



Jlix 



TIT? 



TO PUMP 



l4\ 



1 >' 

 I ! il 



i' n 

 IL!) 



-TO POTENTIAL 



cm. long by 4*5 cm. 



It consisted of a glass tube 40 



diameter. The inner electrode was a quarter-inch brass 

 tube sealed into the glass stopper with sealing-wax, and so 

 adjusted that its lower end, closed air-tight with a brass plug, 

 came about 1*5 cm. from the salt in the bottom of the main 

 tube. It was kept cool by passing dry air under pressure 

 through a glass tube slipped into the metallic tube. The 

 temperature of this electrode rarely exceeded 50-75° C. after 



* There was evidence of chemical action in the blackish appearance 

 of the platinum electrodes. Hot aqua regia dissolved these films, but 

 hot or cold acids or cold aqua regia had little effect. Ammonia readily 

 removed them. Chemical tests, made after several experiments, showed 

 traces of zinc, cadmium and a subiodide of platinum. The lower ends 

 of the electrodes, which rested above the heated salt, became permanently 

 black in colour and brittle after considerable usao-e. 



2 D 2 



