Conductivity  of  Metallic  Oxides.  529 
molecules  with  rise  o£  temperature,  which  is  greater  the  more 
concentrated  the  solution. 
Experiments  on  the  conductivity  of  solutions  in  other 
solvents  show  similar  results.  Walden  and  Centnerschwer  * 
have  investigated  solutions  in  liquid  S02  from  -—76°  C  to  the 
critical  point,  157°  C.  In  all  cases  it  was  found  that  the  con- 
ductivity first  increases  with  rise  of  temperature  and  then 
foils  off,  following  roughly  a  parabolic  formula. 
An  increase  of  conductivity  with  rise  of  temperature  is 
also  found  in  the  case  of  fused  salts.  The  conduction  through 
these  is  electrolytic,  and  the  amount  of  the  ions  liberated  by 
the  current  has  been  shown  to  follow  Faraday's  law  of 
electrolysis  f ;  but  the  increase  of  conductivity  of  fused  salts 
with  temperature  is  not  nearly  so  great  as  that  obtained  in 
the  case  of  heated  metallic  oxides.  The  increase  of  con- 
ductivity with  temperature  of  all  the  oxides  examined  in 
the  present  paper  is  much  more  rapid  than  in  any  known 
case  of  electrolytic  conductivity.  On  heating  a  slab  of  cupric 
oxide  from  12°  C.  to  385°  C,  its  conductivity  increased  5000 
times  ;  and  on  heating  lime  from  763°  C.  to  1466°  C.  the 
conductivity  increased  to  nearly  10G  times  its  value  at  the 
lower  temperature. 
In  cases  of  electrolytic  conductivity  the  increase  of  con- 
ductivity with  rise  of  temperature  is  due  to  the  increased 
mobility  of  the  ions  at  the  higher  temperature.  As  the  oxides 
used  in  these  experiments  remained  solid  throughout  the 
observations,  it  does  not  seem  reasonable  to  suppose  that  the 
mobility  of  the  current-carriers  could  have  increased  by 
the  enormous  amounts  given  above.  The  only  alternative 
explanation  is  that  the  number  of  the  carriers  is  enormously 
increased,  a  supposition  which  is  not  compatible  with  the  idea 
that  the  conductivity  is  electrolytic  ;  for  in  cases  of  electrolytic 
conductivity  increase  of  temperature  decreases  the  degree 
of  ionization,  the  decrease  being  more  rapid  the  more 
concentrated  the  solution. 
If,  on  the  other  hand,  we  consider  the  conductivity  to  be 
metallic  and  the  current  to  be  carried  by  the  negatively 
charged  corpuscles  which  are  wandering  about  in  the  interior 
of  the  oxide,  formed  by  the  dissociation  of  the  metallic  atoms: 
then  the  explanation  is  at  once  to  hand,  for  Welmelt's  work 
has  shown  that  the  number  of  these  corpuscles  emitted  by  the 
oxide  (and,  therefore,  probably  the  number  contained  by  it) 
*  Walden  and   Centnerschwer,   Zeitschr.  phys,   Chem.  xxxix.  d.  513 
(1902). 
t  Lorentz,  Zeitschr.  f.EUMrock.  vii.  p.  277  (1900):  p.  768  (1901). 
