﻿Ionization produced by Carbon at High Temperatures, 199 



varied very much with the condition of the carbon. Curves 

 B to E were carried out with impure carbon, and Gr and H 

 after heating at temperatures between 1500° and 2100° and 

 pressure between 0*005 and 0*05 mm. for a total period of 

 about 40 hours. The values obtained in G and H, as typical 

 experiments, are given in the table below. 









(1. 





Amps, through 

 rod. 



Temp. 



Field 



(voits). 



Ionization, amperes 

 per sq. cm. cathode. 



Pressure in mm. 



80 



1750° 



200 



8-OxlO- 6 



0010 



85 



1810° 



J5 



86x10-6 



0-021 



90 



1850° 



M 



10-6X10- 6 



o-oio 



100 



1950° 



,, 



160X10- 6 



0020 



110 



2050° 



" 



16-0X10- 6 



H. 



0-027 



40 



1250° 



330 





0-001 



45 



1315° 



,, 



1-23 X 10- 8 



0001 



50 



1370° 



,, 



6-17 XlO- 8 



o-ooi 



55 



1440° 





3-29 X 10 -' 



0002 



60 



1500° 



J5 



4-0 XlO- 6 



0-003 



In results G when 110 amperes was applied, a discharge 

 suddenly occurrred, 20 amperes passing through and the 

 voltage across the terminals falling to 50. At these low 

 pressures the discharge began abruptly from the smallest 

 ionization current. Its formation was always very uncertain, 

 and at higher pressures, 0'05 to 0*2 mm._, it generally 

 occurred at lower temperatures (i. e. 1550° to 1850°) and 

 was preceded by a bright glow in the whole space of the 

 flask, or else by blue striations, accompanied by currents up 

 to 0*5 ampere. 



In experiments in which at the low pressures the small 

 ionization current was obtained, it was found that on 

 admitting a small quantity of air to the apparatus the current 

 immediately rose to values similar to those shown in curves 

 B to E. There was no measurable positive ionization pro- 

 duced from the carbon, up to 2000°, when the field (of 200 

 volts) was reversed. 



Summary, 



Measurements were made of the ionization produced by 

 heated carbon at definitely known temperatures between 

 1300° and 2050°, and at various pressures. 



The negative ionization from heated carbon was found to 

 fall continuously, both with reduction of the pressure and 

 with progressive purification of the carbon. 



