544      Mr.  H.  E.  Hurst:  Genesis  of  Ions  hy  Collision  and 
Pressure  2  mms. 
cl  
i 
•2 
•3 
•4 
•5 
X=525 
Q   
3-94 
7-95 
17 
42-7 
a  =6-76 
/3=-08 
n  
394 
8-05 
172 
41-9 
a  =i'665. 
X«  =  349. 
V=344. 
Pressure  1  mm. 
X=525 
3-58 
a  =6-18 
/3=-194 
3-58 
7-15 
•20 
15-9 
16-3 
54-3 
521 
a=-58. 
Xa=304. 
V=300. 
A  satisfactory  agreement  may  be  found  between  these 
tables  and  those  for  the  nitrogen  which  was  first  used. 
Besides  these  experiments  a  number  of  determinations  of 
the  spark-potential  were  made,  for  different  values  of  the 
pressure  and  distance  between  the  plates. 
The  effect  of  mixing  small  quantities  of  oxygen  with  the 
gas  was  also  determined.  The  sparking-potentials  were 
determined  by  connecting  in  series  with  the  parallel  plates 
a  battery  of  small  cells,  a  voltmeter,  and  a  resistance-box. 
In  the  experiments  on  carbon  dioxide  and  the  first 
sample  of  nitrogen  the  total  external  resistance  was  about 
50,000  ohms,  but  in  the  later  experiments  on  nitrogen 
68,000  or  98,000  ohms.  This  increase  of  resistance  raised 
the  sparking-potential  about  2  volts. 
In  all  the  determinations  the  lowest  potential  which  gave 
a  spark  when  ultra-violet  light  of  small  intensity  fell  on  the 
negative  electrode  is  given,  and  this  is  the  potential  V  in  the 
preceding  tables.  But  in  some  of  the  experiments  the  poten- 
tial required  to  give  a  spark  without  the  action  of  ultra-violet 
light  was  also  determined.  After  one  determination  had  been 
made  and  a  spark  had  passed,  it  was  found  necessary  to  wait  a 
