346  The  Stability  of  Iodine  Ointments.  {Am'l°™\^™m- 
of  potassium  iodide  (twice  the  U.  S.  P.  requirement),  12  per  cent, 
of  glycerin  and  76  per  cent,  of  lard.  This  was  assayed  for  its  free 
iodine  content  immediately  after  preparation,  and  found  to  contain 
3.68  per  cent.  Nine  days  later  it  contained  3.70  per  cent.  Another 
specimen  of  the  same  iodine  strength  prepared  from  grade  No.  2  of 
commercial  lard  assayed  3.69  per  cent,  at  the  initial  assay,  and  seven 
days  later  3.40  per  cent.  From  these  experiments  it  seems  likely 
that  the  free  iodine  content  of  the  U.  S.  Pharmacopeia  iodine  oint- 
ment could  be  raised  somewhat  by  increasing  the  proportion  of 
potassium  iodide. 
The  results  of  these  studies  confirm  the  findings  of  Pullen  and 
of  Fried  in  all  essential  particulars.  It  appears  that  during  the 
process  of  manufacture  of  iodine  ointment  about  20  per  cent,  of  the 
free  iodine  goes  into  combination  with  the  fatty  constituents  of  the 
ointment.  On  standing  for  a  month  approximately  an  additional  5 
per  cent,  goes  into  combination,  after  which  there  is  practically  no 
loss  in  free  iodine  content.  In  other  words  iodine  ointment  which 
is  a  month  old  is  a  relatively  stable  preparation.  It  appears  to  make 
no  noticeable  difference  upon  the  rate  and  amount  of  iodine  ab- 
sorption whether  the  lard  from  which  the  ointment  is  made  has  a 
high  or  a  low  iodine  absorption  value.  The  composition  Of  iodine 
ointment,  which  has  been  made  sufficiently  long  to  have  reached 
equilibrium,  is  approximately  as  follows : 
'Free  iodine    3  per  cent. 
Iodine  combined  with  fat    1  per  cent. 
Potassium  iodide    4  per  cent. 
Benzoinated  lard  (containing  iodine)  . . :   80  per  cent. 
The  U.  S.  Pharmacopeia  requirement  that  iodine  ointment  shall 
be  freshly  prepared  when  wanted  appears  to  be  unnecessary.  Prob- 
ably most  pharmaceutical  manufacturers  are  aware  of  this,  for 
many  of  them  include  the  preparation  in  their  trade  lists.  The  pres- 
ence of  an  iodide  appears  to  be  necessary,  to  prevent  practically  all 
of  the  iodine  from  entering  into  combination  with  the  fat.* 
*  In  order  to  determine  whether  the  iodine  which  is  in  combination  with 
fat  is  absorbed  through  the  skin,  a  few  experiments  were  carried  out.  The 
dark-colored  iodine-containing  fat  (obtained  from  the  ointment  and  washed 
free  from  potassium  iodide  by  the  method  described  above)  was  rubbed 
thoroughly  into  the. skin  of  the  forearm.  It  was  allowed  to  remain  for  four 
hours,  after  which  the  limb  was  scoured  with  soap  suds.  Beginning  at  the 
time  of  the  application  the  urine  was  collected  for  forty-eight  hours.  This 
