Ionization from Heated Platinum. 



173 



which was insulated from the remainder o£ the apparatus. 

 The detecting electrode was kept cold by drawing air through 

 a system o£ tubes arranged within the electrode proper. Dry 

 air or other gas was filtered through calcium-chloride towers 

 before admission to the apparatus. The ionization currents 

 were measured by means of a quadrant electrometer. 

 Throughout this paper one division per second represents 

 3'7xl0~ 13 ampere. For further details as to the apparatus 

 and methods of manipulation the reader is referred to the 

 Physical Review, series 2, vol, ii. p. 289. 



III. The Increased Positive Thermionic Currents in Air 



at a given temperature produced by heating 



the wire at higher temperatures. 



A measurable current (one-half of one div. per second) 

 with +200 volts was obtainable at a temperature of 600° C. 

 The temperature was raised by several steps to 628° C. 

 before the ionization currents at -1-200 volts showed any 

 detectable decay with time during twenty minutes testing. 

 At 632° C. a slow decay with time effect was found ; the 

 following is a sample set of data obtained. 



Temperature. 





628° C. 



632° C. 



Current 

 (div. per sec.) 



14 



15 14 13-3 13-5 14 



31 To 21 22 20 19 18 17 



Time 

 (minutes). 







2 4 10 15 20 



\ 2 4 6 8 10 15 20 



The temperature chosen, therefore, as the datum or arbi- 

 trary point at which to test the emission produced by increase 

 of temperature was 628° 0. Curve I. of fig. 1 shows the 

 initial current readings obtained after the wire had been 

 heated for 10 minutes respectively at each of the various 

 temperatures recorded, the wire being connected to earth 

 during the heating, the temperature then being reduced to 

 628° C. at 4- 200 volts. The data for the curves of fig. 1 are 

 given in Table I. 



Curve I. fig. 1 shows maxima after heating at G54° C. 

 and 756° C, the ionization currents being measured at 

 028° C. An attempt will be made in the following pages 

 to show that these maxima indicate the presence in the wire 

 of two substances capable of producing ions, the first beino- 



