518 
Dr.  F.  Horton  on  the  Electrical 
the  various  readings  do  not  fall  so  well  on  the  curves  as  in  the 
former  case.  This  is  no  doubt  due  to  the  causes  already 
mentioned,  and  especially  to  the  action  o£  the  baryta  on  the 
platinum  electrodes.  The  effect  of  this  could  be  seen  in  the 
blackening  of  the  oxide  through  some  considerable  distance 
from  each  surface  of  contact.  Much  importance  cannot,  there- 
fore, be  attached  to  these  values  of  the  conductivity  of  baryta. 
Experiments  showed  that,  as  with  lime  and  magnesia,  some 
electrol}'sis  was  caused  by  the  passing  of  the  current.  Some 
experiments  were  afterwards  made  to  see  whether  any  evolu- 
tion of  gas  at  the  anode  could  be  detected.  These  will  be 
described  later. 
Plumbic  Oxide, 
Some  lead  monoxide  was  melted  in  an  atmosphere  of 
oxygen  (to  prevent  reduction)  and  cast  into  a  slab.  This  was 
filed  up  to  *758  cm.  x  *733  cm.  and  *158  cm.  in  thickness. 
The  following  table  contains  the  values  of  the  conductivity  at 
various  temperatures  after  the  resistance  had  become  small 
enough  to  be  measured. 
1 
Temperature 
Centigrade. 
Resistance  in 
ohms. 
Conductivity  in 
mhos. 
384 
7,000,000 
3-86   XHT8 
420 
2,350,000 
1-15   XHT7 
462 
650.000 
445   X10~7 
.504 
250,000 
1-08   Xl0"6 
539 
128.000 
241   X10~6 
572 
72,000 
3-75  xl0~6 
600 
45,000 
6-00  xl0-c 
646 
13.500 
2-00   xlO-5 
687 
4,050 
6-67   xlO-5 
700 
2,870 
9-39  xlO -5 
757 
730 
3-695X10-4 
_— '87 
330 
84  75  xlO"4 
The  relation  between  the  conductivity  and  the  temperature- 
is  shown  graphically  in  diagram  V. 
When  a  current  of  *001  ampere  was  sent  through  this 
oxide  no  sign  of  electrolysis  could  be  detected,  either  as  a 
liberation  of  gas  or  as  a  polarization  E.M.F.  This  current  is 
much  greater  than  those  used  in  the  determinations  of  the 
conductivity  of  the   oxide.     On  sending  a  current  of  '015 
