302  Iodine  Absorption  of  Essential  Oils.  {Amji0nue'ilSarm- 
the  bottle  in  which  the  digestion  was  taking  place  had  apparently  be- 
come altered  ;  and  a  further  experiment  on  a  weighed  portion  of  pure 
unvulcanized  rubber  conclusively  showed  that  under  these  circum- 
stances the  rubber  absorbed  iodine. 
About  the  same  time  I  found  that  some  eucalyptus  oil  to  which 
aqueous  solution  of  iodine  in  potassium  iodide  was  added  deprived  the 
latter  of  its  iodine,  becoming  at  the  same  time  so  much  heavier  that 
after  repeating  the  treatment  a  few  times  the  oil  sank  to  the  bottom  of 
the  aqueous  liquid.  These  observations  induced  me  to  look  into  such 
literature  as  I  could  find  bearing  on  the  subject  of  iodine  absorption 
by  hydrocarbon  and  essential  oils,  and  this  appeared  to  be  somewhat 
meagre,  consisting  mainly  of  the  statement  that  many  essential  oils  re- 
acted violently  with  solid  iodine,  and  a  suggestion  in  Watt's  "  Dic- 
tionary of  Chemistry/'  vol.  iv.,  p.  190,  that  since  aromatized  waters 
decolorized  solution  of  iodine  by  virtue  of  the  essential  oils  dissolved 
in  them,  it  should  be  possible  to  utilize  the  reaction  as  a  means  of  es- 
timating the  strength  of  such  waters. 
No  experiments  were  recorded  as  to  the  amount  of  iodine  which 
given  weights  of  various  oils  would  absorb  under  these  conditions, 
and  up  to  the  present  time,  so  far  as  I  am  aware,  the  necessary  data 
for  making  this  a  practical  analytical  process  have  not  been  given. 
Having  had  frequent  occasion  lately  to  make  use  of  the  process  de- 
vised by  von  Hiibl  for  estimating  the  iodine  absorption  power  of  fixed 
oils,  it  naturally  occurred  to  me  that  this  useful  analytical  method 
would  yield  results  of  value  when  applied  to  essential  oils,  and  I  pro- 
pose to  bring  some  of  the  results  I  obtained  before  the  members  of  the 
Society  this  evening  in  the  hope  that  they  may  prove  interesting. 
Von  HiibPs  method  of  working  is  the  following : — 25  grams  of 
iodine  and  30  grams  of  mercuric  chloride  are  dissolved  in  absolute  al- 
cohol, and  the  solution  made  up  to  1  litre.  Twenty  cc.  of  this  solu- 
tion are  then  added  to  a  known  weight  (0.4  gram)  of  the  oil  to  be  ex- 
amined, which  has  been  dissolved  in  10  cc.  of  chloroform,  and  the 
mixture  is  allowed  to  stand  some  hours,  after  which  it  is  diluted  with 
15  cc.  of  a  10  per  cent,  solution  of  potassium  iodide,  then  with  150  cc. 
of  water,  and  the  iodine  remaining  in  the  free  condition  is  estimated 
by  titration  with  standard  sodium  hyposulphite  solution.  As  the 
strength  of  the  alcoholic  solution  varies  somewhat  with  its  age  it  is 
necessary  to  perform  a  blank  experiment  with  each  determination  of 
one,  or  of  a  series  of  samples  of  oil,  and  from  the  difference  between 
