ioo  Iodine  and  Potassium  Chlorate.       { Am-^r;1Sarm- 
NOTE  ON  THE  INTERACTION  OF  IODINE  AND 
POTASSIUM  CHLORATE.1 
By  T.  E.  Thorpe,  F.R.S.,  and  George  H.  Perry,  Assoc.  Roy.  Coll.  Science. 
The  interaction  of  iodine  and  potassium  chlorate,  first  employed 
by  Berzelius  for  the  preparation  of  iodine  monochloride,  is  usually 
represented  by  the  equation 
3KCIO3  +  12  =  KC104  +  KC1  +  KIO^  +  IC1  +  02. 
We  find,  however,  that  when  an  intimate  mixture  of  iodine  and 
potassium  chlorate,  in  the  proportions  demanded  by  the  above  equa- 
tion, is  heated,  not  only  is  the  yield  of  iodine  monochloride  invari- 
ably very  far  below  the  theoretical  amount,  but  that  much  of  what 
actually  is  formed  is  converted  into  the  solid  trichloride,  and  that 
free  chlorine  and  more  or  less  iodic  anhydride  are  often  simulta- 
neously formed.  These  facts  seem  to  show  that  the  actual  change 
is  very  imperfectly  indicated  by  the  equation  above  given. 
Careful  quantitative  experiments,  so  arranged  that  the  various 
products  of  the  change,  both  fixed  and  volatile,  could  be  estimated, 
have  shown  that,  in  reality,  the  primary  and  main  reaction  between 
iodine  and  potassium  chlorate  is  a  simple  metathesis:  2KCIO3  -f  I2 
=  2KIO3  +  Cl2.  The  chlorine  so  liberated  attacks  any  iodine  that  is 
not  within  the  "sphere  of  action"  of  the  heated  chlorate,  and  forms 
more  or  less  mono-  and  tri-chloride  of  iodine,  in  amounts  depending 
upon  the  temperature  and  mode  of  heating.  When  care  is  taken 
not  to  heat  the  mixture  to  a  higher  temperature  than  is  actually 
necessary  to  effect  the  above  change,  the  saline  residue  contains 
only  traces  of  potassium  chloride  and  perchlorate,  which  seems  to 
indicate  that  these  substances  are  not  really  products  of  the  direct 
action,  but  are  formed  by  local  superheating  of  the  chlorate,  with 
evolution,  of  course,  of  oxygen,  and  consequent  formation  of  iodine 
pentoxide.  By  careful  management,  it  is  possible  to  convert 
practically  the  whole  of  the  iodine  present  into  potassium  iodate, 
with  the  liberation  of  the  equivalent  amount  of  gaseous  chlorine. 
Iodine  monochloride,  as  is  well  known,  is  readily  dissociated  by 
heat  into  the  trichloride  and  free  iodine.  It  seemed  to  us  interesting 
to  determine  whether  a  solution  of  iodine  monochloride  in  chloro- 
form or  carbon  tetrachloride  would  show  any  indication  of  such 
dissociation  when  allowed  to  diffuse  into  a  quantity  of  the  same 
Journal  of  the  Chemical  Society,  1892,  p.  925. 
