540     Mr.  H.  E.  Hurst :  Genesis  of  Ions  by  Collision  and 
carbon  monoxide  and  oxygen,  some  of  the  oxygen  being  set 
free  as  ozone,  which  would  oxidize  the  zinc  plate.  In  the 
experiments  recorded  above,  all  the  currents  a  were  measured 
before  determining  any  spark-potentials,  and  if  sparking 
took  place  during  these  experiments  it  was  by  accident,  and 
was  only  momentary. 
The  largest  currents  used  were  of  the  order  10~10  ampere, 
so  that  if  electrolysis  takes  place  before  a  spark  passes,  an 
extremely  small  amount  of  gas  is  electrolysed.  Hence  the 
oxidation  effect  on  the  electrodes  is  small,  and  in  the  case  of 
the  experiments  on  air  the  only  noticeable  effect  of  oxidation 
was,  that  the  currents  produced  by  a  given  intensity  of  the 
light  were  proportionately  less.  The  ratios  of  the  currents 
were  unaltered.  That  is  to  say,  oxidation  causes  less  ions  to 
be  given  off  by  the  zinc  plate  under  the  action  of  ultra-violet 
light.  As  to  the  change  of  constitution  of  the  gas,  the  results 
of  the  experiments  show  that  the  spark -potential  can  be 
predicted  from  measurements  of  the  currents  before  a  spark 
passes,  so  obviously  it  is  of  no  importance  whether  the  gas 
remains  as  carbon  dioxide  or  after  passage  of:  the  current 
contains  traces  of  ozone.  If  the  gas  were  electrolysed  in 
quantities  the  last  experiments  of  a  series  should  not  be 
consistent  with  the  first,  but  no  measurable  inconsistency 
was  ever  noticed. 
The  nitrogen  used  in  the  first  set  of  experiments  was 
obtained  from  air  by  passing  air  and  ammonia  over  red-hot 
copper,  the  ammonia  being  in  excess  of  that  required  to 
reduce  the  copper  oxide  formed.  The  nitrogen  so  produced 
was  again  passed  over  red-hot  copper,  and  then  over  caustic 
potash  into  the  drying  apparatus,  where  it  passed  through 
sulphuric  acid,  and  was  finally  dried  by  remaining  in  contact 
with  phosphorus  pentoxide. 
The  following  tables  give  the  results  of  experiments  made 
on  gas  prepared  by  this  method. 
Nitrogen  prepared  by  First  Method. 
Pressure  4  mms. 
d  
!        -2 
•3 
•4 
•5 
X  =  700 
9.    
! 
4-15 
8-58 
18-5 
436 
a  =7-08 
/3—049 
n  
I 
4-15 
8-58 
18-6 
44-3 
r08.  Xa=496.  7=494. 
