576 
Iodine  Absorption  of  Essential  Oils. 
Am.  Jour.  Ptiarm . 
Nov.,  1890. 
solution  of  iodine,  the  process  being  otherwise  conducted  the  same. 
The  results  as  obtained  in  different  periods  of  digestion  are  very 
different  to  those  obtained  by  the  use  of  Hubl's  solution  and  the 
action  may  be  said  to  be  more  rapid  though  it  is  not  uniform  for  all 
oils.  The  results  are  given  in  the  table  for  a  limited  number  of  oils 
as  follows: 
Time  of  Digestion. 
8 
18K 
22 
24 
49 
55 
Hubl's. 
Oil  turpentine,  . 
98 
9i 
80 
397 
"  peppermint, 
46 
48 
50 
113 
"   copaiba,  .  . 
81 
81 
250 
"   coriander,  . 
81 
78 
385 
"   cloves,     .  . 
29 
56 
72 
122 
121 
291 
"  camphor, 
45 
53 
129 
"   limes,  ••  .  . 
"   sassafras,  .  . 
67 
62 
289 
35 
43 
166 
FRACTIONAL  DISTILLATION. 
The  writer  scarcely  looks  for  a  close  degree  of  uniformity  in  the 
"iodine  numbers"  of  essential  oils.  It  is  scarcely  to  be  expected 
that  bodies  of  such  complex  composition  as  these  essential  oils  will 
furnish  "constants"  in  the  ordinary  use  of  the  term.  The  variations 
in  specific  gravity  and  boiling  points,  as  well  as  the  variable  specific 
rotatory  power  of  those  that  are  optically  active,  are  well  known. 
The  iodine  number,  as  already  reported  upon,  is  in  some  cases  quite 
constant.  In  casting  around  for  some  means  of  partially  compen- 
sating for  this,  the  writer  naturally  first  thought  of  fractional  distilla- 
tion. Some  of  the  advantages  which  accrue  from  it  were  pointed  out 
in  a  paper  on  Oil  of  Peppermint,  in  which  it  was  shown  that  a  fraction 
of  one  dram  from  one  ounce  of  oil  of  peppermint  did  not  have 
a  much  higher  absorption  number  than  the  oil  undisturbed  by  frac- 
tional distillation.  The  figures,  as  then  obtained,  were  105  for  the 
natural  oil,  and  this  yielded  a  one-eighth  fraction  having  123  for  the 
number,  while  the  pure  oil,  to  which  was  added  1 3  per  cent,  of  turpen- 
tine, yielded  280  for  its  iodine  number.  At  that  time  experience 
justified  the  statement  that  an  oil  yielding,  from  the  fraction  of  one 
dram  from  one  ounce,  less  than  125,  for  its  iodine  absorption  is  not 
