SYRUP  OF  HYDRIODIC  ACID.  411 
Pharmaceutist,  in  the  vegetable  kingdom  in  the  case  of  vegetable 
syrups,  and  in  the  mineral  kingdom  in  the  case  of  certain  proto- 
salts  of  iron,  where  the  presence  of  sugar  prevents  the  latter 
from  becoming  peroxidized  by  the  absorption  of  oxygen,  as  in 
the  cases  of  the  carbonate,  iodide  and  protonitrate  of  iron.* 
What  method,  therefore,  will  be  best  adapted  for  the  prepara- 
tion of  this  syrup  ?  In  the  usual  way  of  preparing  hydriodic 
acid,  by  passing  sulphuretted  hydrogen  through  iodine  suspended 
in  water,  the  iodine  is  very  apt  to  be  enveloped  in  portions  of 
the  sulphur  that  is  set  free,  and  escape  the  action  of  the  H  S. 
This  being  guarded  against,  a  solution  of  hydriodic  acid  could  be 
obtained,  from  which  a  syrup  might  be  prepared,  if  cautiously 
operated  upon,  that  would  contain  no  free  iodine.  The  repug- 
nance, however,  that  is  usually  felt  by  the  Pharmaceutist  to  the 
employment  of  H  S,  as  the  means  of  preparing  pharmaceutical 
products,  would  render  this  process  objectionable,  although  it 
should  be  found  to  be  in  other  respects  available. 
With  another  means  of  preparing  this  acid,  by  decomposing  a 
solution  of  iodide  of  barium  by  the  equivalent  of  sulphuric  acid, 
and  filtering  to  separate  the  insoluble  sulphate  of  barytes,  as 
the  iodide  of  barium  itself  is  an  unstable  compound,  it  would  be 
necessary  to  prepare  this  salt  at  each  manipulation. 
Assuming,  therefore,  that  if  a  syrup  can  be  prepared  by  Dr. 
Buchanan's  solution  that  shall  contain  no  free  iodine,  it  will 
furnish  the  most  suitable  manner  of  obtaining  this  acid  for 
medicinal  purposes,  I  have  to  propose  the  following  proportions 
for  a  syrup.  It  is  necessary,  however,  to  observe,  as  one  of  the 
conditions  of  success,  that  the  iodide  must  be  free  from  any 
trace  of  iodate  of  potash. 
Of  four  different  samples  of  iodide  that  came  under  my  notice, 
all  gave  a  slight  iodine  reaction  with  solution  of  tartaric  acid  and 
starch.  These,  although  containing  extremely  little  of  the  other 
impurities  usually  found  in  iodide  of  potassium,  were  contaminated 
with  a  minute  portion  of  iodate  of  potash.  They  had  been  pre- 
pared by  what  is  known  as  the  caustic  potash  process,  and  ac- 
cordingly extremely  liable  to  contain  some  undecomposed  iodate. 
*  Syrup  of  protonitrate  of  iron,  Pharmaceutical  Journal,  vol.  xi.,  pages 
329  and  330.    W,  Procter,  Jun.,  and  W.  Livermore. 
