402         PREPARATION  OF  SOLUBLE  IODIDE  OF  STARCH. 
ON  THE  PREPARATION  OF  SOLUBLE  IODIDE  OF  STARCH 
By  M.  Quesneville. 
M.  Quesneville,  who  first  introduced  iodide  of  starch  into 
therapeutics,  advises  the  following  method  of  preparing  it : 
Take  of  starch  of  the  best  quality  (free  from  potato  starch ) 
1050  grammes. 
Iodine,  in  very  fine  powder  (passed  through  a  silk 
sieve)  100  grammes. 
Mix  the  two  powders  carefully,  and  when  the  mixture  is  per- 
fect it  is  to  be  moistened  gradually,  agitating  without  ceasing, 
with  a  mixture  of  400  grammes  of  water  and  100  grammes  of 
alcohol.  The  powder  gradually  deepens  in  color,  and  soon  be- 
comes a  beautiful  black ;  it  is  left  during  15  to  20  days  and  is 
afterwards  dried  in  the  air,  followed  by  the  drying-room  heat. 
The  starch,  if  very  dry,  should  not  be  used  in  larger  proportion 
than  900  grammes. 
When  the  powder  of  iodide  of  starch  is  well  dried,  it  has  no 
odor  of  iodine,  and  contains  exactly  one  tenth  of  its  weight  of 
iodine.  It  is  completely  insoluble  in  water,  and  to  render  it 
soluble  it  is  sufficient  to  heat  it  in  an  enamelled  pan  over  a  very 
gentle  fire,  with  continual  agitation.  This  operation  requires 
but  little  time,  and  the  operator  is  apprized  of  its  completion  by 
the  development  of  a  pungent  odor.  It  is  well  to  try  from 
time  to  time  whether  the  powder  has  become  soluble. 
This  operation,  though  easy,  requires  nevertheless  a  certain 
skill  and  attention,  because  if  heated  too  strongly  the  solution  is 
red  and  has  lost  iodine. 
Iodide  of  starch  powder  obtained  by  this  process  suffices  for 
the  use  of  Pharmacy ;  nevertheless,  if  it  is  desired  to  obtain  it 
more  pure  and  extremely  soluble  in  cold  water  and  always  of  a 
beautiful  violet  blue,  it  is  necessary  to  make  a  warm  concentra- 
ted solution  of  the  strength  of  7  to  8  degrees  of  the  hydrometer 
for  salts,  allowing  it  to  deposit  during  several' days,  decant  the 
solution  and  precipitate  by  adding  only  enough  of  alcohol  to 
precipitate  the  iodide  of  starch.  Put  the  magma  on  a  linen 
cloth,  press  it  as  dry  as  possible  and  complete  the  dessication  on 
