308  Iodine  Absorption  of  Essential  Oils.  {Am-/unl\maim' 
cent  violet  color  when  the  Hiibl  reagent  was  carefully  added  to  their 
chloroformic  solution. 
This  color  changes  gradually  through  blue  into  the  green  first  ob- 
served, which  it  becomes  after  three  or  four  days.  The  red  fluores- 
cence is  well  marked.  The  fact  that  somewhat  similar  colors 
are  produced  by  agency  of  nitric  acid  on  peppermint  oil  is,  of  course, 
familiar,  having  been  pointed  out  by  Professor  Fliickiger  in  1871 
(Pharm.  Joum.,  [3],  i.,  p.  682).  From  such  experiments  as  I  have 
been  able  to  make,  I  conclude  that  the  color  reactions  produced  by 
the  iodine  solution  are  very  much  finer,  and  are  effected  much  more 
'  rapidly  than  those  produced  by  nitric  acid.  The  Japanese  oils  do  not 
give  any  violet  or  blue.  Before  leaving  these  oils,  I  think  it  right  to 
give  the  numbers  assigned  to  such  of  them  as  were  examined  by  Mr. 
Barenthin.  Turpentine,  300  ;  clove,  270  ;  caraway,  265 ;  bergamot, 
260;  juniper,  245;  rosemary,  185;  anise,  164;  lavender,  170;  cala- 
mus, 155;  fennel,  140;  cinnamon,  100  (Archiv  der  Pharmacie,  Oct., 
1886). 
The  solid  substances  examined  were  four.  Three  samples  of 
anethol,  one  of  camphor,  menthol  and  thymol.  In  these  cases,  since 
the  substances  were  regarded  as  of  known  chemical  composition,  and 
not  mixtures,  as  the  oils  very  generally  are,  I  thought  it  probable 
that  if  any  absorption  took  place  it  would  be  in  some  proportion  bear- 
ing a  definite  relation  to  the  molecular  composition.  The  absorption 
in  the  cases  of  camphor  and  menthol  was  so  small  as  to  suggest  the 
presence  of  traces  of  oil,  and  that  the  pure  substances  would  not 
absorb  iodine  at  all.  In  the  case  of  thymol,  there  was  decided 
absorption,  amounting  to  171*5  per  cent,  of  the  thymol  taken.  .Now 
the  formula  of  thymol  being  C10H14O,  if  two  atoms  of  iodine  entered 
into  reaction  with  one  molecule,  the  percentage  absorption  would  be 
169*3,  which  is  very  close  to  that  actually  found.  One  cannot  speak 
with  certainty  until  the  product  has  been  isolated  and  examined,  but 
it  is  probable  that  mon-iodo  thymol  results  from  this  reaction. 
The  anethol  was  simply  separated  by  cold  and  dried  between  bibu- 
lous paper.  Doubtless  there  is  some  adherent  oil,  which  could  be 
separated  by  crystallization  from  alcohol.  When  recrystallized  this 
will  be  subjected  to  a  further  examination.  The  only  conclusion  I 
can  at  present  draw  from  the  very  similar  absorption  equivalents  is 
that  the  composition  of  this  substance  is  the  same,  whether  prepared 
from  star-anise  oil  or  that  of  the  true  aniseed. 
