Am.  Jour.  Pharm.  \ 
December,  1899.  J 
Analysis  of  Essential  Oils. 
569 
merization  sets  in,  with  increase  of  the  specific  gravity  and  decrease 
of  the  solubility,  etc.  Much  quicker  such  changes  will  occur  under 
the  action  of  heat  or  of  chemical  reagents,  and  it  therefore .  cannot 
surprise  that  in  investigations  of  the  components  of  essential  oils, 
in  which  the  use  of  heat  and  of  chemicals  cannot  be  avoided,  often 
bodies  are  found  finally  which  are  quite  different  from  those  origi- 
nally present  in  the  plants.  If  the  bodies  into  which  an  oil  has  been 
separated  by  an  investigator  are  mixed  again,  the  mixture  will  usually 
be  quite  different  from  the  original  oil,  a  sure  proof  that  certain 
constituents  have  undergone  changes  during  their  isolation.  There 
is  even  some  doubt  if  the  oil  which  is  used  for  an  investigation  is 
really  identical  with  the  one  originally  present  in  the  plant,  or  if  it 
has  not  already  undergone  changes  by  the  distillation  with  steam, 
the  process  generally  used  for  the  production  of  essential  oils.  That 
such  changes  actually  occur  is  shown  by  the  fact  that  every  im- 
provement in  the  technical  preparation  of  the  essential  oils  is  accom- 
panied not  only  by  an  increase  of  the  yield,  but  also  by  an  altera- 
tion of  the  properties  of  the  oil.  For  example  :  when  by  the  use 
of  an  improved  distilling  method,  the  time  required  for  the  distilla- 
tion of  cloves  was  reduced  to  about  one-half,  not  only  a  higher 
yield  resulted,  but  the  oil  also  showed  a  finer  fragrance  and  a  mate- 
rially decreased  specific  gravity,  even  considerably  below  the  limits 
required  by  the  U.S. P.,  so  that  for  the  latter  purpose  not  the  natural, 
but  only  fractionated  distillates  were  available.  Evidently  by  the 
former  more  imperfect  process  a  part  of  the  oil,  apparently  just 
substances  of  the  finest  aroma,  had  been  resinified  to  much  less 
volatile  bodies  and  were  thus  lost.  Upon  this  circumstance  is  based 
one  of  the  difficulties  to  fix  definite  requirements  for  the  properties 
of  essential  oils,  as  these  properties  largely  depend  not  only  on  the 
variable  crude  materials  which  have  furnished  the  oils,  but  also  on 
the  process  by  which  the  oils  are  obtained.  If,  for  instance,  as  it 
has  really  been  the  case,  a -chemist  obtains  in  his  laboratory  from 
cloves  7  per  cent,  of  oil,  while  the  improved  technical  distillation 
furnishes  about  18  per  cent.,  it  is  evidently  an  absurdity  to  pro- 
claim the  laboratory  distillate  as  a  standard  for  clove  oil,  because  it 
consists  only  of  the  more  volatile,  respectively  the  more  stable  parts. 
This  inconstancy  of  the  composition  of  essential  oils  renders  it  recom- 
mendable  to  characterize  an  oil  intended  for  analysis  as  completely  as 
possible,  so  that,  in  case  of  different  findings  by  other  investigators, 
