^"^jlTjjs:""- }       On  the  Syrup  of  Ferrous  Iodide,  2  5 1 
Further,  says  Mr.  iMayer,  that  the  officinal  liquor  ferri  iodidi  con- 
tains free  hydriodic  acid,  and  the  quantity  of  iron  in  solution  is  not  suf- 
ficient to  bind  all  iodine. 
This  conclusion  differs  from  my  experiments.  The  aqueous  solution 
of  ferrous  iodide  is  very  liable  to  decomposition.  Ferric  oxide  is  pre- 
cipitated and  free  iodine  is  held  in  solution.  This  is  only  effected  by 
the  formation  of  HI,  which  again  is  decomposed  into  hydrogen  and 
iodine,  and  naturally  the  amount  of  iron  will  decrease  in  the  liquid  as 
the  process  goes  on. 
The  existence  of  a  ferric  iodide  is  very  doubtful.  Ferrous  iodide 
dissolves  free  iodine,  but  the  solution  gives  only  the  reactions  of  a  fer- 
rous salt  and  of  free  iodine.  Freshly- precipitated  ferric  oxide  dissolved 
in  HI  yields  by  heating  only  iodine  and  ferrous  iodide.*  The  aque- 
ous solution  evaporated  in  a  glass  retort  in  a  water-bath  to  syrupy  con- 
sistence gives,  on  cooling,  a  greenish-black,  solid  ferrous  iodide  which, 
dissolved  again,  contains  free  iodine  ;  even  when  passing  a  stream  of 
carbon  dioxide  over  the  evaporating  solution,  I  could  not  succeed  in 
getting  a  greenish  solution  from  the  salt.  As  most  of  the  dry  ferrous 
iodide  of  commerce  is  decomposed,  I  would  recommend  every  apoth- 
ecary to  prepare  it  himself  at  a  minute's  notice,  by  pulverizing  iodine 
with  the  aid  of  a  few  drops  of  alcohol,  and  adding  pulverized  iron  in 
slight  excess,  the  chemical  heat  evaporates  the  few  drops  of  alcohol 
and  leaves  a  hard,  black,  ferrous  iodide. 
Samples  of  syrup,  obtained  from  different  retail  stores  in  San  Fran- 
cisco, showed  a  variation  of  from  10  to  46  grains  of  iodine  to  the 
fluidounce.  In  some  cases  a  syrup  -of  standard  strength  had  evidently 
not  been  aimed  at,  but  in  some  the  deficiency  might  be  explained  by  the 
moisture  of  the  iodine  and  the  carelessness  of  the  operator.  I  would 
recommend  the  following  way  of  making  the  syrup  : 
Test  first  your  resublimed  iodine  for  water  by  heating  a  weighed 
quantity  of  it  in  a  watch-glass  until  fumes  of  iodine  commence  to 
According  to  Mohr  (1858),  a  mixture  of  ferric  chloride  and  iodide  of  potassiums 
impart,  after  some  time,  merely  a  faint  blue  color  to  starch  paste,  and  solution  of  fer- 
rous sulphate  will  dissolve  notable  quantities  of  iodine,  before  the  iodine  and  starch 
reaction  occurs.  Ferric  hydrate,  ether  and  iodine  yield,  according  to  Nickles  (1865), 
a  red  solution,  which  is  precipitated  blue  by  ferrldcyanide  of  potassium,  and  we  may 
add,  that  syrup  of  ferrous  iodide  will  indicate  the  presence  of  a  ferric  salt  by  sulpho- 
cyanide  of  potassium,  before  ferric  oxide  is  deposited.  These  facts  appear  to  us  to 
demonstrate  the  existence  of  ferric  iodide,  although  a  portion  of  the  iodine  is  held 
in  a  loose  com-bination. — Editor  Amer.  Jour.  Phar. 
