Conductivity  of  Metallic  Oxides. 
517 
diagram  IV.,  which  shows  that  the  points  lie  very  nearly 
indeed  on  a  straight  line. 
Experiments  showed  that  the  conduction  of  electricity 
through  magnesia  was  accompanied  by  a  little  electrolysis; 
but  all  the  effects  of  this  were  much  smaller  than  in  the  case 
of  lime. 
The  results  obtained  with  the  other  oxides  experimented  on 
are  very  similar  to  those  for  calcium  and  magnesium,  the 
temperature-conductivity  curves  possessing  in  all  cases 
precisely  the  same  characteristics  as  those  connecting  the 
emission  of  corpuscles  with  the  temperature  of  the  oxide  when 
used  as  the  cathode  in  a  discharge-tube.  The  results  obtained 
with  these  oxides  will  therefore  be  given  more  briefly. 
Baryta. 
This  was  difficult  to  work  with  on  account  of  the  strong 
^chemical  action  it  has  on  platinum  when  heated,  and  because 
of  the  ease  with  which  it  absorbs  moisture  and  carbonic-acid 
gas  from  the  air.  Also,  if  heated  above  a  dull  red  heat,  it 
takes  up  more  oxygen  from  the  air  and  forms  the  dioxide. 
The  numbers  given  in  the  following  table  are  therefore  not 
so  reliable  as  those  given  for  lime  or  magnesia.  The 
dimensions  of  the  piece  of  barium  oxide  used  were  *853  cm. 
by  '843  cm.  and  "467  cm.  thick. 
Temperature 
Centigrade. 
Besistance  in 
ohms. 
Conductivity  in 
mhos. 
307 
646,000 
1-00  X  10_* 
311 
359,000 
1-81  xlO-13 
312 
274,000 
2-37  Xl0~6 
320 
184,000 
3-53  xlO"6 
319 
218,000 
2-98  Xl0~6 
345 
78,400 
8-29x10-" 
355 
10,760 
6-03  xlO-5 
3159 
6,892 
9-43  x  10-"5 
386 
602 
1-08x10-3 
428 
357 
1-82x10-2 
450 
214 
3-04  x  10"  2 
469 
176 
3-70x10-- 
497 
14-1 
4-61  x  10~2 
When  the  conductivities  in  the  above  tabic  arc  plotted 
against  the  corresponding  temperatures,  curves  similar  in 
type  to  those  given  by  lime  and  magnesia  are  obtained  :  but 
