Solubility  of  iodides  in  syrupus  ferri  iodidi.  211 
for  an  hour  ;  the  iron  wire  which  had  been  thrown  in,  however, 
was  covered  with  copper  after  standing  twelve  hours,  and  a 
considerable  precipitate  of  iodide  of  copper  had  been  thrown 
down. 
Freshly  precipitated  iodide  of  copper  was  put  on  a  filter,  and 
syrup  of  iodide  of  iron  filtered  through  it.  The  filtered  liquor 
on  standing  till  next  day  had  precipitated  iodide  of  copper,  and 
the  remaining  solution  still  contained  copper  which  could  be 
thrown  down  by  iron. 
A  syrup  which  does  not  contain  free  iodine  may  be  agitated 
with  copper  turnings  without  dissolving  any  of  it ;  but  when  con- 
taining iodine  in  a  free  state,  it  dissolved  some  copper,  which 
covered  the  iron  that  had  been  afterwards  thrown  in. 
A  much  larger  proportion  of  iodide  of  copper  could  be  dis- 
solved in  the  syrup  if  it  was  kept  at  212°  F.  One  fluidounce 
of  the  syrup  was  put  in  a  water  bath  heated  to  212°  ;  a  quantity 
of  a  solution  containing  2  grs.  of  sulphate  of  copper  had  to  be 
added  before  a  cloudiness  was  obtained.  These  two  grains 
correspond  with  li  grs.  of  iodide  of  copper,  which,  for  the  greater 
part  was  thrown  down  on  cooling. 
Most  experiments  were  performed  with  the  neutral  syrup,  and 
with  another  sample  that  had  decomposed  on  exposure  to  the 
air,  and  contained  some  free  iodine.  The  results  of  the  solu- 
bility of  iodide  of  copper  varied  slightly  in  both  cases,  and  the 
neutral  syrup  seems  to  take  up  rather  more  of  that  insoluble  com- 
pound ;  the  difference  though  is  very  slight. 
It  was  curiosity  now  which  induced  me  to  see  whether  others 
of  the  insoluble  iodides  were  taken  up  by  the  iron  preparation  ; 
and  I  was  surprised  to  find  the  iodides  of  lead,  silver  and  mer- 
cury easily  soluble.    The  green  iodide  of  mercury  turned  blaGk 
and  dark  green  as  soon  as  thrown  in  the  syrup  ;  the  red  iodide 
was  taken  up  in  very  considerable  quantities,  and  after  standing 
several  days,  the  syrup  had  a  voluminous  sediment  of  a  dirty 
blackish  yellow  iodide,  while  the  supernatant  liquid  had  scarcely 
a  brownish  tinge.    Here  the  question  arises  :  how  does  a  reduc- 
tion take  place,  and  what  is  the  result  of  it  ?    May  not  the  for- 
mation of  a  soluble  double  iodide  of  iron  and  mercury  cause  the 
ready  solubility  of  the  red  iodide  of  the  metal,  which,  through 
the  influence  of  the  atmosphere,  is  decomposed  again  ? 
