Conduct iviti/  of  Metallic  Oxides.  519 
ampere  through  the  oxide  for  a  short  time,  and  then  con- 
necting it  up  to  a  delicate  galvanometer,  a  feeble  polarization 
current  was  indicated  :  but  this  was  much  smaller  than  those 
Diagram  V. — Showing  increase  of  conductivity  of  Plumbic  (hide 
with  temperature. 
400  500  600°       700" 
T£fliPER/JTU/f£         C£rtT/G/?AP£  . 
observed  in  the  experiments  with  the  oxides  of  thefalkalire 
earths.  The  temperature  of  the  plumbic  oxide  during  these 
experiments  was  780°  C;  the  polarization  was  still  smaller  at 
lower  temperatures.  I 
Bismuth  Trioxide. 
Slabs  of  bismuth  trioxide  were  prepared  in  a  manner  similar 
to  that  employed  with  plumbic  oxide.  Some  pure  trioxide 
was  melted  in  a  stream  of  oxygen  and  cast  into  a  slab  which 
was  filed  up  to  the  required  size.  The  sample  from  which 
the  numbers  given  in  the  following  table  were  obtained  was 
•77  cm.X*77  cm.  and  -202  cm.  thick. 
