Am.  jour.  Pharm.  j     jjie  Stability  of  Iodine  Ointments. 
Aug.  1917.      >  ->  ' 
345 
A  portion  of  the  ointment  which  had  been  made  for  nearly  three  months 
was  shaken  in  a  separator  with  chloroform  and  a  dilute  mixture  of  potas- 
sium iodide  and  sodium  thiosulphate  solutions.  After  all  of  the  free  iodine 
had  been  removed  the  chloroformic  solution  of  the  fats  was  washed  several 
times  with  a  very  dilute  solution  of  sodium  thiosulphate.  The  chloroformic 
solution  was  filtered,  evaporated  and  the  residue  dried  over  sulphuric  acid.* 
The  separated  fat  was  then  tested  for  iodine  by  Kendall's  method.12 
It  was  found  to  contain  iodine  in  considerable  amounts,  but  quanti- 
tative determinations  were  not  made. 
The  Pharmacopeia  of  the  Netherlands  directs  that  iodine  oint- 
ment shall  contain  3  per  cent,  of  potassium  iodide  and  2  per  cent, 
of  iodine  instead  of  equal  proportions  (4  per  cent,  of  each)  as  pre- 
scribed by  the  U.  S.  Pharmacopeia.  Likewise  the  French  Pharma- 
copeia directs  that  10  per  cent,  of  potassium  iodide  and  only  2  per 
cent,  of  iodine  shall  be  used.  Both  of  these  pharmacopeias  use 
water  instead  of  glycerin  as  the  solvent.  Loose  combinations  of 
iodine  and  potassium  iodide,  such  as  is  represented  by  the  compound 
having  the  formula  KI3,  have  been  described.  The  quantity  of 
potassium  iodide  prescribed  by  the  U.  S.  Pharmacopeia  for  the 
preparation  of  iodine  ointment  is  not  sufficient  to  form  such  a  com- 
pound as  KI3  with  all  of  the  iodine  directed  to  be  used.  Since  some 
of  the  pharmacopeias  use  larger  proportions  of  potassium  iodide 
(more  than  sufficient  to  form  the  compound,  KI3),  it  seemed  worth 
while  to  determine  whether  an  ointment  containing  a  greater  pro- 
portion of  potassium  iodide  than  that  required  by  the  U.  S.  Pharma- 
copeia would  be  more  stable  than  the  official  article.  Accordingly 
a  specimen  was  prepared  to  contain  4  per  cent,  of  iodine,  8  per  cent. 
*  The  resultant  fatty  residue  was  of  a  brownish-green  color.  It  no 
longer  had  either  the  taste,  color  or  odor  of  lard.  It  v/as  noted  that  the 
fats,  after  removal  by  this  method  from  the  freshly  prepared  ointment',  were 
nearly  white.  As  the  ointment  aged  the  fat  became  successively  darker  in 
color. 
12  The  method  depends  upon  the  conversion  of  all  of  the  iodine  com- 
pounds into  iodate  by  fusion  with  sodium  hydroxide  and  oxidation  with 
potassium  nitrate.  The  melt  is  dissolved  in  water,  a  little  sodium  bisulphite 
added,  the  solution  cooled  and  neutralized  with  phosphoric  acid,  using  methyl 
orange  as  indicator.  An  excess  of  bromine  water  is  added,  and  the  mixture 
boiled  to  expel  carbon  dioxide  and  bromine.  A  little  sodium  salicylate  is 
added,  the  solution  cooled,  an  excess  of  potassium  iodide  added,  and  the  lib- 
erated iodine  titrated  with  tenth-normal  sodium  thiosulphate  in  the  usual 
way.  One  sixth  of  the  iodine  found  is  obtained  from  the  material  assayed, 
the  balance  being  furnished  by  the  potassium  iodide  added.  Jour.  Biochem., 
19,  251  (1914)- 
