324 



Mr. John Alien Harlcer 



[Feb. 9, 



described the pressure remained atmospheric, and alternating current 

 was employed for heating. Access of air to the interior of the 

 furnace was prevented by windows at each end, perforated as 

 required. 



In the early experiments we inserted within the carbon furnace 

 tube two insulated carbon electrodes, one of them being hollow, so 

 that a Siemens optical pyrometer could be sighted through it. The 

 two electrodes were joined externally to an ammeter and a battery of 

 cells (see Fig. 2), and we proceeded to determine current- voltage 



ArTi|3ere3 



Lo?. Amperes' 

 0-2 ■ 



0-2- 



0-4- 



Temf). 



1700° 



1900 



2100" 2300 C. 



Fig. 5. — The Fumj Line Curve shows a Relation between Ionization 

 Current and Temperature, for an Applied Potential of 2 Volts 

 ON A 1 CM. Gap between the Electrodes. The dotted straight line is 

 plotted from the log. of the current and the temperature. 



curves at various furnace temperatures. Some of these curves are 

 shown in Fig. 4 for an electrode gap of 1 cm. No appreciable current 

 could be detected below 1400° C. with applied potentials up to 8 volts, 

 but as the temperature rose the current rapidly increased until at 

 2500° or more currents up to 10 amperes were recorded. At the 

 lower temperatures the currents soon attain what appear to be 

 saturation values. At higher temperatures there is a linear relation 

 between potential and current. As the length of the gap increased 

 the current diminished at a regular rate ; but the decrease was small. 



