Am.  Jour.  Pharm.  \ 
October,  1896.  J 
Oil  of  Mojiarda  Fistulosa. 
543 
Titrimetric  Estimation  of  Carvacrol. — Five  grammes  of  the  oil,  di- 
luted with  10  c.c.  of  petroleum  ether,  were  repeatedly  shaken  with 
5  per  cent,  sodium  hydroxide  solution  until  no  more  of  the  oil  was 
dissolved.  The  oil  was  then  tested  for  carvacrol  by  Fliickiger's 
reaction,  which  consists  in  heating  a  few  drops  with  chloroform  and 
a  little  solid  sodium  hydroxide,  when,  if  carvacrol  is  present,  a 
wine-red  color  will  appear.  The  absence  of  color  will  show  that  all 
of  the  carvacrol  has  been  removed  by  the  soda  solution.  The  alka- 
line solution  of  carvacrol  was  made  up  with  5  per  cent,  solution  to 
100  c.c.  or  200  c.c,  as  the  case  required.  To  10  c.c.  of  this  solution 
a  sufficient  quantity  of  ^  iodine  volumetric  solution  was  added  to 
convert  all  of  the  carvacrol  into  carvacrol  iodide.  To  effect  this  a 
slight  excess  of  iodine  was  necessary.  In  order  to  know  when  a 
sufficient  quantity  of  iodine  had  been  added,  a  few  drops  were  re- 
moved from  time  to  time,  and  added  to  some  diluted  hydrochloric 
acid.  In  this  way  free  iodine  can  be  detected  as  soon  as  it  is  in 
excess.  The  mixture  was  then  made  up  to  500  c.c.  and  filtered. 
The  carvacrol  iodide  did  not  separate  readily,  but  separation  could 
be  induced  by  agitation  of  the  milky  liquid.  To  100  c.c.  of  the 
filtrate,  diluted  hydrochloric  acid  was  added,  and  the  liberated  iodine 
estimated  with  sodium  thiosulphate  volumetric  solution.  The 
quantity  of  ^  sodium  thiosulphate  required,  multiplied  by  5,  gives 
the  quantity  of  iodine  solution  that  had  been  added  in  excess. 
From  this  the  amount  of  iodine  required  can  be  easily  found. 
Every  molecule  of  carvacrol  requires  4  atoms  of  iodine,  therefore, 
every  cubic  centimetre  of  ~  iodine  volumetric  solution  is  equivalent 
to  0-0037415  c.c.  of  carvacrol. 
Only  a  few  of  the  specimens  of  oil  were  tested  according  to  this 
method. 
