THE  AMERICAN 
JOURNAL  OF  PH^4MA 
JUNE,  i9i5  Uj 
THE  ESTIMATION  OF  FREE  AClh^m^^VfXY- 
CHLORIDE  SOLUTION. 
The  test  for  oxychloride  and  for  free  aeid  in  solution  of  ferric 
chloride  as  given  in  the  Netherlands  Pharmacopoeia  differs  from  that 
in  the  United  States,  the  Belgian,  and  the  German  Pharmacopoeia. 
The  test  is  this :  "  When  a  mixture  of  I  Cc.  of  the  solution  with 
5  Cc.  of  water  is  boiled  for  one  minute,  the  liquid  must  be  turbid 
after  cooling." 
The  other  pharmacopoeias  mentioned  direct  the  boiling  with 
sodium  thiosulphate,  with  this  difference :  that  the  U.  S.  P.  requires 
that  no  brownish-red  precipitate  of  ferric  hydroxide  should  separate, 
the  other  two  permitting  a  slight  precipitate. 
Three  of  the  pharmacopoeias  permit  a  slight,  but  not  definite, 
amount  of  oxychloride;  the  U.  S.  P.  proscribes  this,  but  permits  free 
hydrochloric  acid.  •  , 
With  different  specimens  of  ferric  chloride  solution  the  test  of 
the  Netherlands  Pharmacopoeia  gives  very  different  degrees  of  tur- 
bidity; I  therefore  endeavored  to  determine  the  acidity  of  the  solu- 
tions. 
The  test  of  the  U.  S.  P.  could  not  be  employed  for  this  purpose, 
for  when  applied  to  a  solution  with  free  hydrochloric  acid  the  liber- 
ated thiosulphuric  acid  decomposes  in  the  hot  solution  into  free 
sulphur,  sulphur  dioxide,  and  water. 
At  the  ordinary  temperature  the  conversion  of  ferric  thiosulphate 
into  ferrous  tetrathionate  proceeds  very  slowly.  I  have  found  that 
the  reaction  is  very  much  accelerated  by  the  addition  of  a  few  drops 
of  a  cupric  chloride  solution.  This  becomes  evident  by  the  following 
test:  Into  each  of  two  100  Cc.  flasks  place  2  Cc.  ferric  chloride 
By  Dr.  G.  Romijn,  'S  Hertogenbosch,  Holland. 
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