Conductivity produced by Heating Salts. 735 



With a~pressure of 220 mm. of mercury and an average 

 temperature of 190° 0., a saturation-current was obtained. 



The readings were all taken over an interval of one minute, 

 and the temperature was nearly constant. Saturation was 

 obtained with F charged to 160 volts when testing for 

 positive ions. At still higher voltages a large increase 

 in the leak took place. This is probably due to fresh ions 

 being formed by collisions, since the voltages then used 

 were nearly sufficient to produce sparking. 



The apparatus was next arranged so that the temperature 

 could be kept at a constant value during the observations, 

 and the pressure was still further reduced to 20 mm. of 

 mercury. The temperature was now 198° C, and varied less 

 than 1° C. A saturation-current was now obtained in the 

 case of the positive ions with a difference of potential of 

 110 volts. Hence at lower pressures a saturation-current is 

 obtained with lower voltages. 



It was found that the voltage required to produce saturation 

 was greater in the case of the positive ions than of the negative 

 ions — a result which can be explained if the positive ions move 

 at a slower rate in the same electric field than the negative 

 ions. This was afterwards proved to be the case. 



