December ,^90™' }    Preparing  Pharmaceutic  Chemicals.  581 
METHODS  FOR  PREPARING  SOME  PHARMACEUTIC 
CHEMICALS. 
By  Dr.  Gunnar  Heikel. 
Acidum  Hydriodicum. 
The  official  U.  S.  P.  process  for  making  this  acid  gives  a  product, 
which  may  be  pure  enough  for  most  medicinal  purposes,  although 
it  is  far  from  being  a  chemically  pure  acid,  owing  to  the  fair  solubil- 
ity of  potassium  bitartrate  in  hydriodic  acid,  and  to  the  addition  of 
an  appreciable  amount  of  potassium  hypophosphite.  The  allow- 
able residue  after  evaporation,  which  according  to  the  latest  revision 
of  the  U.  S.  P.  can  be  as  high  as  8.3  per  cent.,  shows  clearly  that  the 
degree  of  purity  is  very  low  indeed. 
Another  method  for  preparing  diluted  hydriodic  acid,  which  is 
found  in  most  of  the  text-books,  is  to  conduct  sulphuretted  hydrogen 
gas  into  water  in  which  iodine  in  fine  subdivision  is  suspended. 
The  reaction  is  thus : 
I2  +  H2S  =  2HI  +  S 
In  the  author's  hands  this  method  has  proven  unsatisfactory,  as 
the  iodine  soon  becomes  entirely  coated  with  the  liberated  sulphur 
and  further  action  consequently  ceases.  If,  however,  the  io'dine  be 
dissolved  in  carbon  disulphide  or  chloroform,  the  solvent  readily 
takes  up  the  sulphur  and  the  hydriodic  acid  goes  into  the  super- 
natant water,  which  after  separation  from  the  solvent,  is  evaporated 
down  to  the  desired  concentration.  The  action  of  sulphuretted- 
hydrogen-gas  upon  a  solution  of  iodine  is  also  much  more  rapid 
than  upon  the  iodine  in  solid  form.  Nevertheless,  this  method  of 
preparation  is  slow,  and  the  working  with  the  bad-smelling  sulphu- 
retted hydrogen  is  very  unpleasant.  When  a  larger  quantity  of  the 
acid  is  required  the  use  of  this  method  is  almost  out  of  question. 
Hydriodic  acid  of  a  high  degree  of  concentration,  used,  for  ex- 
ample, as  a  reducing  agent  for  organic  compounds,  is  made  by  the 
action  of  phosphorus  on  iodine  in  the  presence  of  water.  The 
method  being  both  tedious  and  expensive,  and  besides  somewhat 
dangerous,  is  not  suitable  for  pharmaceutical  purposes. 
A  good,  simple  method  for  preparing  an  almost  chemically  pure 
acid,  used  in  numerous  instances  by  the  author,  is  as  follows :  A 
solution  of  iron  iodide  is  prepared  in  the  usual  way  from  iodine 
and  iron-filings.    To  this  solution  somewhat  more  than  the  equiva- 
