DECAY  OF  GUTTA  PERCHA.  557 
from  it,  I  give  the  results  of  some  experiments  to  which  I  refer 
in  this  month's  Photographic  Journal,  considering  that  they  may 
be  useful  to  the  manufacturing  chemist. 
On  treating  powdered  witherite  with  iodide  of  iron,  we  do  not 
get  a  complete  decomposition  even  after  prolonged  ebullition. 
To  decompose  it,  native  carbonate  is  generally  heated  with  char- 
coal, which  accelerates  the  decomposition,  as  it  requires  a  violent 
heat  to  drive  olf  the  carbonic  acid  from  the  witherite  alone. 
If  we  keep  a  mixture  of  witherite  and  half  its  weight  of  iron 
filings  or  borings  (those  from  malleable  iron  are  preferable)  at  a 
slow  red  heat  for  some  time,  in  an  iron  or  black  lead  crucible, 
the  carbonate  is  decomposed,  carbonic  oxide  being  liberated. 
The  heat  must  not  be  sufficient  to  run  the  iron.  If  the  roasting 
has  been  carried  far  enough,  the  contents  of  the  crucible  are 
found  to  be  strongly  alkaline.  On  adding  water  and  iodine,  and 
then  boiling  for  some  time,  the  iodine  forms  iodide  of  barium, 
combining  first  with  the  excess  of  iron,  and  is  then  converted 
into  the  barium  salt.  The  residual  precipitate,  which  seems 
somewhat  similar  in  composition  to  artificial  magnetic  oxide  of 
iron,  is,  from  its  density,  easily  washed.  The  liquors,  on  evapo- 
ration, yield  crystals  of  iodide  of  barium,  which  on  recrystalliza- 
tion  are  chemically  pure. 
This  process  is  much  preferable  to  that  of  making  hydriodic 
acid  and  dissolving  the  carbonate  in  it,  particularly  when  ope- 
rating on  a  large  quantity  Ibid, 
DECAY  OF'  GUTTA  PERCHA. 
From  the  reports  of  Mr.  E.  Highton  on  the  state  of  the  under- 
ground wires  of  the  British  Electric  Telegraph  Company,  pub- 
lished in  the  Journal  of  the  Society  of  Arts,  it  appears  that 
wherever  the  wires  had  passed  near  the  roots  of  oak  trees  they 
had  failed,  whilst  in  other  parts,  only  a  few  yards  distant,  they 
were  perfectly  sound.  On  examining  the  soil  a  whitish  looking 
plant  was  detected,  resembling  the  spawn  of  the  mushroom,  or 
some  other  fungus ;  the  plant  had  spread  over  and  around  the 
wooden  trough,  covering  it  with  a  whiteness  resembling  white- 
wash, and  wherever  it  had  touched  the  gutta  percha  wires  the 
gutta  percha  was  rotten ;  a  yellowish-green  fungus,  of  which  this 
