Am.  Jour.  Pharm, ) 
May,  1882.  j 
Syrup  of  HyariodiG  Acid. 
241 
all  the  experiments  tend  towards  the  same  conclusion,  so  that  there  is 
reason  in  the  weaker  strength  of  the  syrup  now  being  advertised. 
Glycerin,  it  may  be  stated,  has  little  restraining  effect  on  the  decom- 
position, probably  owing  to  its  hygroscopic  properties. 
As  to  the  best  manner  of  preparing  the  acid,  I  have  tried  nearly  all 
the  methods,  and  in  the  end  have  always  come  back  to  the  decompo- 
sition of  sulphuretted  hydrogen  with  free  iodine  as  represented  by  the 
following  equation  :  2H2S  +  2I2  =  S2+4HI.  Decomposition  of  iodide 
of  barium  with  sulphuric  acid  might  afford  a  suitable  means  of 
obtaining  it,  were  it  not  for  these  two  objections,  namely,  that  it  neces- 
sitates the  personal  preparation  of  the  iodide  of  barium,  and,  second, 
the  distillation  of  the  product  after  decomposition.  The  methods 
recommended  in  text-books  of  decomposing  iodide  of  potassium  with 
iodine  and  phosphorus  in  the  presence  of  a  small  quantity  of  water, 
or  of  distilling  the  acid  from  iodine  and  phosphorus  in  the  presence 
of  a  large  quantity  of  water,  are  both  unsatisfactory.  In  the  first 
case  there  is  always  more  or  less  of  an  element  of  risk,  and,  moreover, 
the  strength  of  the  finished  product  requires  in  every  case  to  be  esti- 
mated ;  while  the  second  method  has  always  proved  in  ray  hands  an 
admirable  one  for  obtaining  a  variety  of  compounds  of  which  phos- 
phoretted  hydrogen  may  be  taken  as  typical.  In  preparing  a  stronger 
solution,  say  of  four  or  five  grains  iodine  to  each  drachm,  by  the  sul- 
phuretted hydrogen  process  some  little  difficulty  may  at  first  be 
experienced  in  effecting  complete  decomposition  of  the  iodine.  The 
iodine  is  not  soluble  to  any  extent  in  water,  nor  can  it  conveniently  be 
kept  suspended  in  the  water  so  as  to  allow  the  sulphuretted  hydrogen 
to  act  upon  it.  If  put,  therefore,  into  the  bottle  through  which  the 
sulphuretted  hydrogen  gas  is  being  passed,  it  simply  lies  at  the  bottom ^ 
the  particles  shortly  adhere  and  form  a  plastic  mass ;  this  in  turn  soon 
becomes  coated  with  sulphur,  and  practically  the  iodine  ceases  to 
dissolve.  To  obviate  this  I  take  advantage  of  the  solubility  of  iodine 
in  both  hydriodic  acid  and  sulphuretted  hydrogen,  and  instead  of 
passing  the  gas  on  to  the  iodine  I  pass  it  through  the  iodine  solution.. 
To  do  this  without  waste,  two  bottles  are  required,  the  one  being 
attached  to  the  gas  generator  and  the  other  preparing  for  it.  The 
iodine  (in  a  glass  mortar)  is  rubbed  down  Avitli  the  solution  from  the 
sulphuretted  hydrogen  generator  until  it  is  saturated,  when  it  is  again 
transferred  to  the  generator  and  the  other  withdrawn  from  it,  in  turn 
to  be  saturated  with  the  iodine.  In  this  way  the  process  can  be  carried 
on  with  the  least  waste  either  of  time  or  material. — The  Chemist  and 
Druggist,  February  15,  1882. 
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