588 Mr. A. E. Garrett on Positive Electrification 



At about 200 volts there are indications that the current 

 is nearly saturated, yet on slightly increasing the voltage, it 

 again rises very rapidly and does not actually reach its 

 saturation value until over 300 volts are put on. 



On the other hand, the curve obtained with negative ions 

 is quite a smooth one and does not show any indication of 

 saturation at a voltage lower than 220, nor does any further 

 increase in current take place if the voltage is raised from 

 220 to 656. This is shown in fig. 6, in which the upper 

 curve represents the current due to positive ions, the lower 

 curve that due to negative ions at different voltages. 



Fiff. 6. 





























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200 220 240 260 280 300 320 340 360 



This, taken in conjunction with the fact that a current is 

 obtained at the second electrode when 656 volts are put on 

 the first, suggests that either two classes of positive ions are 

 present, or else neutral doublets. The former is rendered 

 unlikely on account of the constancy of the current which 

 passes between the electrodes after 320 volts is reached. 



X. Further Evidence of Doublets. 



In order to test whether neutral pairs as well as ions are 

 shot off from the heated salt when surrounded by gas at 

 a low pressure, the apparatus shown in the next diagram 

 was used. 



The essential part of this apparatus consists of a long glass 

 tube, in one end of which is a Faraday cylinder F, and in 

 the other end the heated salt on the platinum foil S. 



During the experiment the foil was kept at a positive 

 potential sufficiently high to prevent negative ions from 

 leaving the salt. The wire gauze P was also kept at such a 

 positive potential as to drive back any positive ions which 

 have passed through the earthed metal tube E. 



The apparatus was evacuated to an air-pressure of about 



