produced in Gases by Rontgen Rays fyc. 439 



To observe the effect of different gases at different pressures 

 on the uranium-conductance-zero we used the small piece of 

 uranium mounted in a glass bulb as described in § 2. The 

 precautions taken in filling the bulb with gas are also described 

 in the same section. 



The uranium was connected to the insulated terminal of 

 the electrometer and the zinc cylinder to the case of the 

 electrometer. In the following table the results obtained 

 with air, hydrogen, and oxygen are given. 



Difference of potential between the uranium-conductance-zero 



Pressure, 





aim uue metallic iwu. 





in mm. 



760 



Hydrogen. 

 + '17 of a volt 

 (iu about a minute : 

 afterwards steady). 



Oxygen. 

 + •105 of a volt 

 ; (in about a minute ; 

 afterwards steady). 



Air. 

 + •11 of a volt 

 (in about a minute 

 afterwards steady). 



193 



+ •12 of a volt 

 (in about a minute : 

 afterwards steady). 







66 



+ •05 of a volt 



(6 minutes). 



+ •11 of a volt 

 (3 minutes). 





8 



+ •04 of a volt 

 (8 minutes). 







2 





+ •10 of a volt in 



27 minutes. 



<Tt>W 



•05 of a volt in ! 



28 minutes. 





The uranium-conductance-zero between mutually insulated 

 uranium and zinc differs much less from the metallic zero 

 than it did with the arrangement described in § 7. This is 

 probably due to the oxidation of the zinc of the zinc cylinder. 

 The conductance zero, however, it will be noticed is approxi- 

 mately the same in all three gases. 



§ 10. Voltage necessary to produce a Spark between Uranium 

 and Zinc at different atmospheric pressures when the dis- 

 tance apart was constant. 



The small piece of uranium before referred to was used. 

 The distance between it and the surrounding zinc cylinder 

 was about 2 or 3 millim. We found that at ordinary atmo- 

 spheric pressure sparking took place in air at 4800 volts. 

 At 232 millim. pressure the potential necessary to produce a 

 spark fell to between 1500 and 2000 volts. At 127 millim. 

 it had fallen to between 1100 and 1300 volts. At 54 millim. 

 it was 700 volts ; at 7 millim. 420 volts. At about jo l do 

 millim. the voltage had risen aaain to 2000 volts. 



