210        SOLUBILITY  OF  IODIDES  IN  SYRUPUS  FERRI  IODIDI. 
ON  THE  SOLUBILITY  OF  IODIDES  IN  SYRUPUS  FERRI  IODIDI, 
By  Jno.  M.  Mmsch. 
Recently  a  syrup  of  iodide  of  iron  came  into  my  hands  "which 
had  been  obtained  of  a  manufacturing  chemist.  As  it  had  under- 
gone decomposition  and  contained  free  iodine,  I  was  desirous  of 
neutralizing  the  same  so  as  to  have  it  fit  for  use.  Having  put 
some  fragments  of  iron  into  it,  the  syrup  was  set  aside  for 
several  weeks,  when,  on  examining  it,  I  was  surprised  to  find 
the  iron  covered  with  copper.  From  what  source  was  that  metal 
present,  and  why  was  it  not  precipitated  by  the  iodine  as  iodide 
of  copper,  which  is  considered  insoluble  ?  These  questions  pre- 
sented themselves,  and,  in  order  to  solve  them,  a  series  of  ex- 
periments were  undertaken  with  the  following  result : — • 
The  syrup,  which  in  the  above  way  had  been  deprived  of 
copper,  still  contained  free  iodine.  One  fluid  ounce  was  mixed 
with  a  solution  of  sulphate  of  copper,  two  grains  of  which  had 
been  dissolved  in  100  grs.  of  water ;  every  drop  of  this  solution 
produced  a  thick  precipitate,  which,  however,  dissolved  on  be- 
ing agitated  with  the  syrup,  which  remained  perfectly  clear 
after  16  grains  of  the  solution  had  been  added ;  the  17th  grain 
produced  a  slight  cloudiness,  which  was  little  increased  on  ad- 
dition of  the  18th  grain,  the  syrup  still  remaining  transparent ; 
but  20  grains  caused  such  a  precipitate  that  the  syrup  looked 
very  turbid,  and  had  lost  all  transparency.  Thus  it  will  be  seen 
that  one  fluidounce  was  capable  of  decomposing  J  gr.  of  sul- 
phate of  copper,  and  holding  the  formed  iodide  of  copper  in  so- 
lution. -J  grain  of  sulphate  contains  l-12th  gr.  of  metallic  copper 
corresponding  with  J  gr.  of  its  iodide. 
(Cu=31-6;  CuO,  S03+5  HO  =124-6;  Cu2I=  189-5) 
Thirty  grains  of  iron  and  three  grains  of  copper,  both  in  the 
state  of  fine  filings,  were  agitated  with  eight  grains  of  iodine 
and  the  necessary  quantity  of  water.  A  greyish  matter  floated 
in  the  liquid  corresponding  in  all  physical  properties  with  a  pre- 
cipitate of  iodide  of  copper.  The  liquid  was  filtered  into  a  vial 
containing  enough  sugar  to  make  one  ounce  of  syrup,  which  was 
of  a  greenish  unsuspicious  appearance,  and  did  not  separate  any 
copper  on  a  bright  spatula  having  been  left  in  contact  with  it 
