Posit ice Ionization from Hot Salts. 



C91. 



at low pressures than has been observed in any other case by 

 the tube method, but the seusitiveness is still much less than 

 that obtained in most cases by the strip method with the 

 various salts which were tested by it. 



Fi". 5. 



100 



15 



FffESSUftE (a*MS.) 



At the end of: the last experiment the thermionic current 

 was 1*75 X 10 " 7 amp. when the apparatus was pumped right 

 down to 0'002 mm. Air was let in to a pressure of 1 mm. 

 when the emission increased to 3'2 x 10~ 7 amp. On in- 

 creasing the pressure to atmospheric the steady emission was 

 found to have diminished to 5*5 x 10~ 8 amp. When the air 

 was pumped out again the emission remained fairly constant 

 until a pressure of about 10 mm. was reached, when it fell off 

 steadily until the value 1*75 Xl0 -8 amp. was reached at 

 0*004 mm. A current-pressure curve was then taken imme- 

 diately and gave the following values : — 



Pressure (mm.) 



Positive Emiss. 

 (I = l'25xl0 _9 amp.) 



Actual Temperature... 775° C. 



•004 -66 1-63 29 5*7 8-3 20 94 7*75 4-48 P83 -87 -004 



} 14 16 17 18 19 19 17 15 15 13 10-5 10 12 



775° C. 775° C. 



The mean curve obtained from these numbers only varies 

 from 13 to 17 between '004 and 25 mm., and exhibits a steady 

 rise from to 6 mm., after which it remains practicallv 

 constant. The substance had been heated for about 13 hours 

 at the close of the last experiment. It was now heated in a 



