314        PATENT  FOR  OBTAINING  IODIDE  OF  POTASSIUM. 
PATENT  GRANTED  TO  F.  M.  LYTE,  FOR  IMPROVEMENTS  TN 
OBTAINING  IODIDE  OF  POTASSIUM,  WHEN  TREATING  CERTAIN 
METALS. 
This  invention  consists  in  the  discovery,  that  when  the  chlo- 
rides, or  some  soluble  salts  of  certain  metals  are  placed  in  contact 
with  solutions  containing  mixed  iodides  and  chlorides,  double  de- 
composition ensues,  and  insoluble  metallic  iodides  are  formed,  and 
that,  by  continuing  the  addition  of  the  chlorides,  this  continues 
so  long  as  any  soluble  iodide  remains  in  the  solution  ;  also  that 
the  insoluble  iodide  can  afterwards  be  converted  into  a  metal  and 
a  soluble  iodide  by  any  of  the  processes  in  use  at  present  for  the 
decomposition  of  metallic  chlorides,  as  in  refining  silver.  For 
instance,  the  patentee  refines  silver,  and  at  the  same  time  pro- 
duces iodide  of  potassium  from  such  solutions  as  bittern,  or  mat- 
ters which  contain  these  mixed  iodides  and  chlorides.  Having 
dissolved  the  silver  in  nitric  acid,  and  precipitated  it  with  a 
soluble  chloride,  as  chloride  of  silver,  he  divests  it  of  copper  by 
washing  with  water.  He  then  projects  the  chloride  so  produced 
into  the  solution  of  mixed  chlorides  and  iodides,  and  continues 
the  addition,  with  frequent  stirring,  till,  on  adding  a  portion  of 
the  chloride  of  silver  to  a  test-sample  of  the  liquid,  it  ceases  to 
become  yellow.  Then,  to  ensure  all  the  silver  being  converted 
into  iodide,  he  adds  a  very  small  portion  more  of  the  mixed  salts, 
so  that  there  may  be  a  small  excess  of  iodine  in  the  solution, 
rather  than  a  trace  of  chlorine  in  the  precipitate.  The  addition 
of  ammonia  facilitates  the  decomposition :  so  also  does  heating 
the  liquid.  The  iodide  of  silver  thus  produced  is  converted  into 
iodide  of  potassium  and  metallic  silver  by  projecting  it  when  com- 
pletely desiccated,  into  a  crucible  containing  fused  carbonate  of 
potash,  according  to  the  method  now  in  use  for  the  reduction  of 
the  chloride ;  but  by  this  process  iodide  of  potassium  is  formed, 
instead  of  the  chloride  as  formerly, — a  valuable  product,  instead 
of  a  product  of  little  value. 
By  adding  a  soluble  salt  of  lead  to  the  mixed  salts  till  all  the 
iodine  is  precipitated,  and  decomposing  the  iodide  thus  formed 
by  the  same  method,  iodide  of  potassium  is  formed,  which  may 
be  dissolved  and  purified  by  recrystallization. 
The  periodide  of  mercury  (a  most  splendid  pigment)  is  pro 
duced  by  adding  the  bichloride  of  mercury  to  the  mixed  salts. 
