The  Electrical  Conductivity  of  Metallic  Oxides.        505 
Summary  of  Results. 
(1)  For  rapidly  alternating  currents  a  flame  containing  an 
alkali-salt  vapour  behaves  like  an  insulating  medium  having 
a  high  specific  inductive  capacity. 
(2)  The  conductivity  of  different  alkali-salt  vapours  in  a 
flame  for  rapidly  alternating  currents  as  measured  by  the 
apparent  capacity  of  platinum  electrodes  immersed  in  the 
flame  varies  as  the  square  root  of  the  conductivity  of  the 
same  salt  vapours  for  steady  currents.  This  result  confirms 
the  view  that  the  negative  ions  from  all  salts  have  the  same 
velocity. 
(3)  The  apparent  capacity  varies  nearly  inversely  as  the 
square  root  of  the  maximum  applied  P.D. 
(-1)  The  apparent  capacity  is  nearly  independent  of  the 
number  of  alternations  per  second. 
(5)  The  apparent  capacity  is  nearly  independent  of  the 
distance  between  the  electrodes. 
(6)  The  results  (1)  to  (5)  are  in  agreement  with  the  ionic 
theory  of  the  conductivity  of  the  flame  for  rapidly  alternating 
currents  when  the  velocity  of  the  positive  ions  and  the  inertia 
and  viscous  resistance  to  the  motion  of  the  negative  ions  are 
neglected  in  comparison  with  the  effects  due  to  the  number 
of  ions  per  c.c. 
(7)  The  apparent  capacity  per  sq.  cm.  area  of  the  electrodes 
is  equal,  according  to  the  theory  just  mentioned,  to  <\/ne/ti'xV0, 
where  n  is  the  number  of  positive  ions  per  c.c,  e  the  charge 
on  one  ion,  and  V0  the  maximum  applied  P.D. 
(8)  Not  more  than  one  molecule  in  30  salt  molecules  is 
ionized  at  any  instant  in  the  flame,  but  each  molecule  is 
probably  ionized  and  recombines  several  million  times  per 
second. 
(9)  The  steady  currents  observed  through  salt  vapours  in 
flames  are  very  far  from  the  maximum  possible  currents  cor- 
responding to  the  number  of  ions  produced  per  second. 
XLIII.  The  Electrical  Conductivity  of  Metallic  Oxides.  By 
F.  HORTON,  D.Sc,  B.A.,  Fellow  or  St.  Johns  College, 
Cambridge  *. 
THE  theory  of  electrolytic  dissociation  has  furnished  a 
simple  explanation  of  conductivity,  in  electrolytes,  by 
assuming  that  the  current  is  carried  as  a  stream  of  electric 
charges  by  the  ions  into  which  a  certain  proportion  of  the 
molecules   of  an  electrolyte  are  dissociated.     Conduction  in 
*  Communicated  by  Prof.  J.  J.  Thomson. 
Phil.  Mag.  S.  6.  Vol.  11.  No.  64.  April  1906.  2  L 
